Solvent and acid stable membranes, methods of manufacture thereof and methods of use thereof inter alia for separating metal ions from liquid process streams

ABSTRACT

Solvent and acid stable ultrafiltration and nanofiltration membranes including a non-cross-linked base polymer having reactive pendant moieties, the base polymer being modified by forming a cross-linked skin onto a surface thereof, the skin being formed by a cross-linking reaction of reactive pendant moieties on the surface with an oligomer or another polymer as well as methods of manufacture and use thereof, including, inter alia separating metal ions from liquid process streams.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application Ser. No.61/193,962, filed Jan. 13, 2009 and entitled “MODIFIED SOLVENT STABLEMEMBRANES HAVING IMPROVED PROPERTIES” and to U.S. Provisional PatentApplication Ser. No. 61/144,459, filed Jan. 14, 2009 and entitled“METHOD FOR SEPARATING METAL IONS FROM LIQUID PROCESS STREAMS” thedisclosures of which are hereby incorporated by reference and priorityof which is hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5)(i).

FIELD OF THE INVENTION

The present invention relates to membranes having enhanced solvent andacid stability, methods of manufacture thereof and methods of usethereof.

BACKGROUND OF THE INVENTION

The following documents, the contents of which are hereby incorporatedby reference, are believed to represent the current state of the art:

U.S. Pat. Nos. 4,014,798; 4,214,020; 4,238,306; 4,238,307; 4,246,092;4,477,634; 4,517,353; 4,584,103; 4,604,204; 4,659,474; 4,690,765;4,690,766; 4,704,324; 4,720,345; 4,753,725; 4,767,645; 4,778,596;4,833,014; 4,889,636; 4,894,159; 4,911,844; 4,952,220; 5,024,765;5,028,337; 5,032,282; 5,039,421; 5,049,282; 5,057,197; 5,067,970;5,087,338; 5,116,511; 5,151,182; 5,152,901; 5,158,683; 5,205,934;5,265,734; 5,272,657; 5,282,971; 5,304,307; 5,310,486; 5,430,099;5,458,781; 5,476,591; 5,547,579; 5,587,083; 5,597,863; 5,599,506;5,733,431; 5,858,240; 5,945,000; 5,961,833; 6,086,764; 6,132,804;6,156,186; 6,159,370; 6,165,344; 6,355,175; 6,536,605; 6,733,653;6,827,856; 6,835,295; 6,843,917; 7,077,953 and 7,138,058.

U.S. Patent Publication Nos. 2003/0089619; 2007/0125198; 2008/0000809;2008/0069748 and 2009/0101583.

European Patent Nos. 0 422 506 and 0 574 957.

Published PCT Application Nos. WO 94/27711, 95/30471, 99/23263,99/40996, 00/50341, and 03/35934.

“The Chemistry of the Cyano Group”, F. C. Schaefer ed. Z. Rappoport,Interscience, New York, chapter 6, p. 239-305, (1970).

“The Chemistry of Amidoximes and Related Compounds”, F. Eloy and R.Lenaers, Chem. Rev., 62, p. 155, (1962).

H. Schonhorn and J. P. Luongo, J. Adhesion Sci. Technol., Vol. 3, N4,pp. 227-290, (1989).

A. Taguet, B. Ameduri and B. Boutevin, J. Adv. Polym. Sci., 184, p.127-211 (2005).

The Solution Diffusion Model: A Review, J. G. Wijmans, R. W. Baker, J.Membrane Science, 1995, vol. 107, pp. 1-21.

Platt et al., J. Membrane Science 239 (2004) 91-103.

A. Warshawsky et al., J. of Polymer Sci., Part A: Polymer Chemistry,Vol. 28, p. 2885, pp 3303-3315 (1990).

A. Noshay and L. M. Robertson, J. Appl. Polym. Sci., Vol. 20, p. 1885(1976).

M. D. Guiver, O. Kutowy and J. W. A. Simon, Polymer, 30, p. 1137 (1989).

Quing Shi et al. J. of Membrane Sci., 319, p. 271 (2008).

“Handbook of Industrial Membranes”, K. Scott, Elsevier Publishers,section 2.1, pp. 187-269.

“Basic principles of membrane technology”, M. Mulder, pp. 465-473(1996).

“Membranes for industrial wastewater recovery and reuse”, Simon Judd &Bruce Jefferson (eds), Elsevier, Chapter 2 (2003)

Applied Surface Science, 253, Issue 14, 2007, pp. 6052-6059, You-Yi Xuet al.

SUMMARY OF THE INVENTION

The present invention seeks to provide membranes having enhanced solventand acid stability, methods of manufacture thereof and methods of usethereof.

There is thus provided in accordance with a preferred embodiment of thepresent invention a polymeric semipermeable membrane including anon-cross-linked base polymer having reactive pendant moieties, the basepolymer being modified by forming a cross-linked skin onto a surfacethereof, the skin being formed by a cross-linking reaction of reactivependant moieties on the surface with an oligomer or another polymer.

Preferably, the polymeric semipermeable membrane also includes asubstrate underlying the base polymer. Additionally, the substrate is awoven or non-woven textile substrate.

In accordance with a preferred embodiment of the present invention themembrane is free-standing.

Preferably, the cross-linked skin is hydrophilic. Alternatively, thecross-linked skin is hydrophobic.

In accordance with a preferred embodiment of the present invention thesurface is a top surface of the base polymer. Alternatively, the surfaceincludes a top surface of the base polymer and other exposed surfaces ofthe base polymer.

Preferably, the polymeric semipermeable membrane also includes ananofiltration layer formed over at least a portion of the cross-linkedskin. Additionally, the nanofiltration layer is covalently bonded to thecross-linked skin.

In accordance with a preferred embodiment of the present invention thereactive pendant moieties are a species selected from the groupconsisting of halogen and nitrile.

Preferably, the reactive pendant moieties are intrinsic to the basepolymer. Additionally, the base polymer is selected from the groupconsisting of polyvinylidene fluoride, acrylonitrile polymer andcopolymers thereof. Additionally, the base polymer includespolyacrylonitrile.

In accordance with a preferred embodiment of the present invention thereactive pendant moieties are added to the outer surface of the basepolymer by a chemical process. Preferably, the base polymer is a polymerincluding a plurality of repeating sulfone groups. Additionally, thebase polymer is selected from polysulfones, polyether sulfones andpolyphenylene sulfones. Most preferably, the base polymer is polyethersulfone.

In accordance with a preferred embodiment of the present invention thechemical process is an oxidation reaction. Preferably, the oxidationreaction is an ozonation reaction. Alternatively, the chemical processis a chlorosulfonation reaction. Preferably, the chlorosulfonationreaction is carried out in a solvent including glacial acetic acid or amixture of acetic acid with at least one non-polar solvent.

Preferably, the another polymer is selected from polyethylenimine andpolyvinyl alcohol. More preferably, the another polymer ispolyethylenimine.

In accordance with a preferred embodiment of the present invention thepolymeric semipermeable membrane is an ultrafiltration membrane or amicrofiltration membrane.

Preferably, the cross-linking reaction is effected at elevatedtemperature utilizing a solution of the oligomer or another polymer,optionally followed by a drying step at elevated temperature.Additionally, the drying step is effected by air drying at elevatedtemperature.

In accordance with a preferred embodiment of the present invention thepolymeric semipermeable membrane is a polyacrylonitrile ultrafiltrationmembrane and the another polymer is polyethylenimine. Alternatively, thepolymeric semipermeable membrane is a polyvinylidene fluorideultrafiltration membrane and the another polymer is polyethylenimine.

Preferably, the polymeric semipermeable membrane is characterized byhaving improved stability compared to the non-modified membrane in anaggressive environment including at least one of the group consisting ofacid media, basic media, organic solvents, oxidizing species, elevatedtemperatures and elevated pressure. Additionally, the aggressiveenvironment includes at least one organic solvent in which thenon-modified membrane dissolves or is damaged.

There is also provided in accordance with another preferred embodimentof the present invention a method of forming a polymeric semipermeablemembrane including providing a non-cross-linked base polymer havingreactive pendant moieties and effecting a cross-linking reaction betweenthe reactive pendant moieties on a surface of the base polymer with anoligomer or another polymer, thereby forming a cross-linked skin on thesurface of the base polymer.

Preferably, the surface is a top surface of the base polymer.Additionally or alternatively, the surface includes a top surface of thebase polymer and other exposed surfaces of the base polymer.

In accordance with a preferred embodiment of the present invention themethod further includes forming a nanofiltration layer over at least aportion of the cross-linked skin. Additionally, the forming includescovalently bonding the nanofiltration layer to the cross-linked skin.

Preferably, the reactive pendant moieties are a species selected fromthe group consisting of halogen and nitrile.

In accordance with a preferred embodiment of the present invention thebase polymer is selected from the group consisting of polyvinylidenefluoride, acrylonitrile polymer and copolymers thereof. Preferably, thebase polymer includes polyacrylonitrile.

In accordance with a preferred embodiment of the present invention themethod also includes adding reactive pendant moieties to the outersurface of the base polymer by a chemical process in order to providethe non-cross-linked base polymer having reactive pendant moieties.Preferably, the base polymer is selected from polysulfones, polyethersulfones and polyphenylene sulfones. More preferably, the base polymeris polyether sulfone.

In accordance with a preferred embodiment of the present invention thechemical process is an oxidation reaction. More preferably, theoxidation reaction is an ozonation reaction. Alternatively, the chemicalprocess is a chlorosulfonation reaction. Preferably, thechlorosulfonation reaction is carried out in a solvent including glacialacetic acid or a mixture of acetic acid with at least one non-polarsolvent.

Preferably, the another polymer is selected from polyethylenimine andpolyvinyl alcohol. More preferably, the another polymer ispolyethylenimine.

In accordance with a preferred embodiment of the present invention thecross-linking reaction is effected at a first elevated temperatureutilizing a solution of the oligomer or another polymer.

Preferably, the first elevated temperature is in the range of 50-100° C.More preferably, the first elevated temperature is in the range of70-90° C.

Preferably, the cross-linking reaction is carried out for 5-32 hours.More preferably, the cross-linking reaction is carried out for 10-20hours.

Preferably, the concentration of the oligomer or another polymer in thesolution is in the range of 2-10%. More preferably, the concentration ofthe oligomer or another polymer in the solution is 4%.

In accordance with a preferred embodiment of the present invention themethod is followed by a drying step at a second elevated temperature.Preferably, the second elevated temperature is in the range of 70-120°C. Preferably, the drying step is effected by air drying.

In accordance with a preferred embodiment of the present invention thecross-linking reaction includes reacting amine groups with nitrilegroups to form amidine groups. Preferably, the polymeric semipermeablemembrane is a polyacrylonitrile ultrafiltration membrane and the anotherpolymer is polyethylenimine.

Preferably, the cross-linking reaction includes reacting primary andsecondary amino groups with halocarbon groups to form imine and tertiaryamino groups. Preferably, the polymeric semipermeable membrane is apolyvinylidene fluoride ultrafiltration membrane and the another polymeris polyethylenimine.

There is provided, in accordance with an embodiment of the invention, amethod for separating a metal from a metal-containing liquid stream, theliquid stream being acidic, basic or organic solvent-based, the methodincluding providing a nanofiltration membrane for which at least one ofthe following (a), (b), (c)(i), (c)(ii) and (c)(iii) is true:

-   (a) the nanofiltration membrane contains a matrix that has been    formed from    -   (i) at least one di-, tri- or tetra-halo substituted diazine or        triazine-containing monomer, oligomer or polymer, and    -   (ii) at least one multifunctional amine having a molecular        weight in the range of 400 to 750,000, provided that at least        one of the di-, tri- or tetra-halo substituted diazine or        triazine-containing monomer, oligomer or polymer is not a di- or        triazine monomer which is substituted only by Cl;-   (b) the nanofiltration membrane is a composite nanofiltration    membrane which contains a matrix that is covalently bound to an    underlying UF support membrane;-   (c)(i) after exposure of the nanofiltration membrane to 75% sulfuric    acid at 60° C. for 300 hours, the nanofiltration membrane removes at    least 70% of the copper ions at a flux greater than 1 gfd from a    feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the feed    solution is applied to the membrane at a feed pressure of 600 psig    and a temperature of 25° C.;-   (c)(ii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 90° C. for 180 hours, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.;-   (c)(iii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 45° C. for 60 days, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.;    and permeating at least a portion of the metal-containing liquid    stream through the nanofiltration membrane, whereby to obtain a    permeate which is reduced in the metal relative to the    metal-containing liquid stream.

In some embodiments, the liquid stream is an acidic metal-containingliquid stream. In some embodiments, the liquid stream is a basicmetal-containing liquid stream. In some embodiments, the liquid streamis an organic solvent-based metal-containing liquid stream.

In some embodiments, the metal is copper. In some embodiments, thecopper is in the form of a divalent ion.

In some embodiments, (a) is true. In some embodiments, (b) is true. Insome embodiments, both (a) and (b) are true. In some embodiments, both(a) and at least one of (c)(i), (c)(ii) and (c)(iii) are true. In someembodiments, both (b) and at least one of (c) (i), (c)(ii) and (c)(iii)are true. In some embodiments, (a), (b) and at least one of (c)(i),(c)(ii) and (c)(iii) are true. In some embodiments, (c)(i) is true. Insome embodiments, (c)(ii) is true. In some embodiments, (c)(iii) istrue.

In some embodiments, the matrix has been formed on an underlyingultrafiltration or microfiltration membrane. In some embodiments, theunderlying UF or MF membrane is not a polyethersulfone membrane. In someembodiments, the underlying UF or MF membrane is not a polysulfonemembrane. In some embodiments, the underlying UF or MF membrane is not apolyvinylidene fluoride membrane. In some embodiments the underlyingmembrane is a UF membrane that is covalently attached to a support. Insome embodiments the support is a non-woven support. In someembodiments, the matrix is covalently bound to the underlying UF or MFmembrane.

In some embodiments, after the exposure the flux under the recitedconditions is at least 6 gfd.

In some embodiments, after exposure of the NF membrane to 75% sulfuricacid at 60° C. for 1000 hours, the membrane exhibits a glucose rejectionof at least 95% at a flux of at least 10 gfd.

In some embodiments, after the exposure at least 80% of the copper ionsare removed under the conditions recited. In some embodiments, at least90% of the copper ions are removed under the conditions recited.

In some embodiments, the halo-substituted diazine or triazine-containingmonomer or oligomer is selected from the group consisting of:

wherein:R¹ is independently selected at each occurrence from bromo, chloro,iodo, fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selectedat each occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R² is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R³ is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R⁴ is selected from H, bromo, chloro, fluoro, —NHR⁵, —OR⁵ and SR⁵,whereinR⁵ is independently selected at each occurrence from H, optionallysubstituted alkyl and optionally substituted aryl; andR⁸ is independently selected at each occurrence from —NH₂— and—NH-A-NH—, wherein A is selected from C₁₋₂₀ aliphatic moieties, C₆₋₁₀aromatic moieties, and combinations thereof;provided that at at least two occurrences, R¹, R², R³ and R⁴, takentogether, are selected from bromo, chloro and fluoro, and furtherprovided that when both R¹ and R² on a single ring are Cl, at least oneof R³ and R⁴ is not Cl.

In some embodiments, the multifunctional amine has a molecular weight ofin the range of 400 to 750,000.

In some embodiments, the matrix is formed by a process which includesproviding an asymmetric base ultrafiltration membrane which at one facethereof has pores of smaller diameter than at the opposite face;providing a solution containing at least one di-, tri- or tetra-halosubstituted diazine or triazine-containing monomer, oligomer or polymer,at least one multifunctional amine having a molecular weight in therange of 400 to 750,000, and optionally, at least one supplementalcross-linker; and bringing the solution into contact with the face ofthe ultrafiltration membrane having smaller pores under superatmosphericpressure for a time sufficient to effect covalent bonding of the atleast one di- or tri-halo substituted diazine or triazine-containingmonomer, oligomer or polymer and the at least one multi-functionalamine. In some embodiments, the time and pressure are sufficient toeffect covalent bonding at of the least one di- or tri-halo substituteddiazine or triazine-containing monomer, oligomer or polymer, the atleast one multi-functional amine, and the surface of the pores of theultrafiltration membrane. In some embodiments, prior to the contacting,the ultrafiltration membrane has been modified to facilitate covalentbonding to the surface thereof. In some embodiments, prior to thecontacting, the ultrafiltration membrane has been modified by forming across-linked ultrafiltration matrix on the surface thereof, on which theNF matrix is then formed. In some embodiments, the formation of thenanofiltration membrane further includes, after the contacting, heatingthe ultrafiltration membrane. In some embodiments, the multifunctionalamine is selected from the group consisting of polyethylenimine,polyvinylamine, polyvinylanilines, polybenzylamines,polyvinylimidazolines, and amine-modified polyepihalohydrins. In someembodiments, the supplemental cross-linker is selected from the groupconsisting of 2,4,6-trichloro-s-triazine, 4,6-dichloro-2-sodiump-sulfoanile-s-triazine (4,6-dichloro-2-p-anilinesulfonic acid sodiumsalt-s-triazine), 4,6-dichloro-2-diethanolamine-s-triazine and4,6-dichloro-2-amino-s-triazine.

In some embodiments the matrix is covalently bound to the underlyingsupport membrane.

In some embodiments the matrix is attached to an underlying UF supportmembrane which has been prepared as described in co-pending U.S.Provisional Patent Application No. 61/193,962.

In some embodiments, the matrix includes cationic functional groups.

In some embodiments, the matrix has a density of from about 0.5 g percm³ to about 2.0 g per cm³. In some embodiments, the matrix has adensity of from about 0.7 g/cm³ to about 1.7 g/cm³. In some embodiments,the matrix has a density of from about 0.8 g/cm³ to about 1.6 g/cm³. Insome embodiments, the mass to area ratio of the matrix is from about 20to about 200 mg/m². In some embodiments, the mass to area ratio of thematrix is from about 30 to about 150 mg/m².

In some embodiments, the method further includes recovering the metalwhich has been separated from the acidic metal-containing liquid stream.

In some embodiments, the method further includes forming the acidicmetal-containing liquid stream by providing a metal containing ore andleaching metal from the ore by contacting the ore with an acidic liquid.In some embodiments, the acidic liquid is sulfuric acid.

There is also provided, in accordance with an embodiment of theinvention, a metal which has been separated from a metal-containingliquid stream by a method in accordance with embodiments of theinvention.

There is also provided, in accordance with an embodiment of theinvention, an apparatus for separating a metal from a metal-containingliquid stream, the liquid stream being acidic, basic or organicsolvent-based, the apparatus including a nanofiltration membrane forwhich at least one of the following (a), (b), (c)(i), (c)(ii) and(c)(iii) is true:

-   (a) the nanofiltration membrane contains a matrix that has been    formed from    -   (i) at least one di-, tri- or tetra-halo substituted diazine or        triazine-containing monomer, oligomer or polymer, and    -   (ii) at least one multifunctional amine having a molecular        weight in the range of 400 to 750,000, provided that at least        one of the di- or tri-halo substituted diazine or        triazine-containing monomer, oligomer or polymer is not a di- or        triazine monomer which is substituted only by Cl;-   (b) the nanofiltration membrane is a composite nanofiltration    membrane which contains a matrix that is covalently bound to an    underlying UF support membrane;-   (c)(i) after exposure of the nanofiltration membrane to 75% sulfuric    acid at 60° C. for 300 hours, the nanofiltration membrane removes at    least 70% of the copper ions at a flux greater than 1 gfd from a    feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the feed    solution is applied to the membrane at a feed pressure of 600 psig    and a temperature of 25° C.;-   (c)(ii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 90° C. for 180 hours, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.;-   (c)(iii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 45° C. for 60 days, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.

In some embodiments, (a) is true. In some embodiments, (b) is true. Insome embodiments, both (a) and (b) are true. In some embodiments, both(a) and at least one of (c)(i), (c)(ii) and (c)(iii) are true. In someembodiments, both (b) and at least one of (c)(i), (c)(ii) and (c)(iii)are true. In some embodiments, (a), (b) and at least one of (c)(i),(c)(ii) and (c)(iii) are true. In some embodiments, (c)(i) is true. Insome embodiments, (c)(ii) is true. In some embodiments, (c)(iii) istrue.

In some embodiments, the apparatus further includes a housing whichhouses the nanofiltration membrane. In some embodiments, the housingincludes at least one inlet port and at least one outlet port. In someembodiments, the housing includes at least two outlet ports. In someembodiments, the at least two outlet ports are separated such that oneof the at least two outlet ports is in fluid communication with thepermeate stream that exits the membrane and the other of the at leasttwo outlet ports is in fluid communication with the retentate streamthat is retained by the membrane.

In some embodiments, the matrix has been formed on an underlyingultrafiltration or microfiltration membrane. In some embodiments, theunderlying UF or MF membrane is not a polyethersulfone membrane. In someembodiments, the underlying UF or MF membrane is not a polysulfonemembrane. In some embodiments, the underlying UF or MF membrane is not apolyvinylidene fluoride membrane. In some embodiments, the matrix iscovalently bound to the underlying UF or MF membrane.

In some embodiments, after the exposure the flux under the recitedconditions is at least 6 gfd.

In some embodiments, after exposure of the NF membrane to 75% sulfuricacid at 60° C. for 1000 hours, the membrane exhibits a glucose rejectionof at least 95% at a flux of at least 10 gfd.

In some embodiments, the di-, tri- or tetra-halo substituted diazine ortriazine-containing monomer or oligomer is selected from the groupconsisting of:

wherein:R¹ is independently selected at each occurrence from bromo, chloro,iodo, fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selectedat each occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R² is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R³ is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R⁴ is selected from H, bromo, chloro, fluoro, —NHR⁵, —OR⁵ and SR⁵,whereinR⁵ is independently selected at each occurrence from H, optionallysubstituted alkyl and optionally substituted aryl; andR⁸ is independently selected at each occurrence from —NH₂— and—NH-A-NH—, wherein A is selected from C₁₋₂₀ aliphatic moieties, C₆₋₁₀aromatic moieties, and combinations thereof;provided that at at least two occurrences, R¹, R², R³ and R⁴, takentogether, are selected from bromo, chloro and fluoro, and furtherprovided that when both R¹ and R² on a single ring are Cl, at least oneof R³ and R⁴ is not Cl.

In some embodiments, the matrix is formed by a process which includesproviding an asymmetric base ultrafiltration membrane which at one facethereof has pores of smaller diameter than at the opposite face;providing a solution containing at least one di- or tri-halo substituteddiazine or triazine-containing monomer or oligomer, at least onemultifunctional amine having a molecular weight in the range of 400 to750,000, and optionally, at least one supplemental cross-linker; andbringing the solution into contact with the face of the ultrafiltrationmembrane having smaller pores under superatmospheric pressure for a timesufficient to effect covalent bonding of the at least one di- ortri-halo substituted diazine or triazine-containing monomer or oligomerand the at least one multi-functional amine. In some embodiments, thetime and pressure are sufficient to effect covalent bonding at of theleast one di- or tri-halo substituted diazine or triazine-containingmonomer or oligomer, the at least one multi-functional amine, and thesurface of the pores of the ultrafiltration membrane. In someembodiments, prior to the contacting, the ultrafiltration membrane hasbeen modified to facilitate covalent bonding to the surface thereof. Insome embodiments, the formation of the nanofiltration membrane furtherincludes, after the contacting, heating the ultrafiltration membrane. Insome embodiments, the multifunctional amine is selected from the groupconsisting of polyethylenemine, polyvinylamine, polyvinylanilines,polybenzylamines, polyvinylimidazolines, and amine-modifiedpolyepihalohydrins. In some embodiments, the supplemental cross-linkeris selected from the group consisting of 2,4,6-trichloro-s-triazine,4,6-dichloro-2-sodium p-sulfoanile-s-triazine(4,6-dichloro-2-p-anilinesulfonic acid sodium salt-s-triazine),4,6-dichloro-2-diethanolamine-s-triazine and4,6-dichloro-2-amino-s-triazine. In some embodiments, the matrixincludes cationic functional groups.

There is also provided, in accordance with an embodiment of theinvention, nanofiltration membrane of which at least one of thefollowing (a), (b), (c)(i), (c)(ii) and (c)(iii) is true:

-   (a) the nanofiltration membrane contains a matrix that has been    formed from    -   (i) at least one di- or tri-halo substituted diazine or        triazine-containing monomer, oligomer or polymer, and    -   (ii) at least one multifunctional amine having a molecular        weight in the range of 400 to 750,000, provided that at least        one of the di- or tri-halo substituted diazine or        triazine-containing monomer, oligomer or polymer is not a di- or        triazine monomer which is substituted only by Cl;-   (b) the nanofiltration membrane is a composite nanofiltration    membrane which contains a matrix that is covalently bound to an    underlying UF support;-   (c)(i) after exposure of the nanofiltration membrane to 75% sulfuric    acid at 60° C. for 300 hours, the nanofiltration membrane removes at    least 70% of the copper ions at a flux greater than 1 gfd from a    feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the feed    solution is applied to the membrane at a feed pressure of 600 psig    and a temperature of 25° C.-   (c)(ii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 90° C. for 180 hours, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.;-   (c)(iii) after exposure of the nanofiltration membrane to 20%    sulfuric acid at 45° C. for 60 days, the nanofiltration membrane    removes at least 70% of the copper ions at a flux greater than 1 gfd    from a feed solution of 8.5% CuSO₄ in 20% sulfuric acid when the    feed solution is applied to the membrane at a feed pressure of 600    psig and a temperature of 25° C.

In some embodiments, (a) is true. In some embodiments, (b) is true. Insome embodiments, both (a) and (b) are true. In some embodiments, both(a) and at least one of (c)(i), (c)(ii) and (c)(iii) are true. In someembodiments, both (b) and at least one of (c)(i), (c)(ii) and (c)(iii)are true. In some embodiments, (a), (b) and at least one of (c)(i),(c)(ii) and (c)(iii) are true. In some embodiments, (c)(i) is true. Insome embodiments, (c)(ii) is true. In some embodiments, (c)(iii) istrue.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified illustration of an ultrafiltration membraneconstructed and operative in accordance with an embodiment of thepresent invention;

FIG. 2A is a computer-enhanced photomicrograph of one example of theultrafiltration membrane of FIG. 1;

FIG. 2B is a computer-enhanced photomicrograph of another example of theultrafiltration membrane of FIG. 1;

FIGS. 3A and 3B are simplified illustrations of chemical reactions whichtake place in the manufacture of the ultrafiltration membrane of FIG. 1in accordance with one embodiment of the present invention and whichproduce covalent bonding;

FIGS. 4A and 4B are simplified illustrations of chemical reactions whichtake place in the manufacture of the ultrafiltration membrane of FIG. 1in accordance with another embodiment of the present invention and whichproduce covalent bonding;

FIG. 5 is a simplified illustration of a nanofiltration membraneconstructed and operative in accordance with an embodiment of thepresent invention;

FIG. 6 is a computer-enhanced photomicrograph of one example of thenanofiltration membrane of FIG. 5;

FIGS. 7A and 7B are simplified illustrations of chemical reactions whichtake place in the manufacture of the nanofiltration membrane of FIG. 5in accordance with one embodiment of the present invention and whichproduce covalent bonding; and

FIGS. 8A and 8B are simplified illustrations showing the acid stabilityof two types of nanofiltration membranes constructed and operative inaccordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIG. 1, which is a simplified illustration ofan ultrafiltration membrane constructed and operative in accordance withan embodiment of the present invention. As illustrated in FIG. 1, thereis provided a polymeric semipermeable membrane including anon-cross-linked base polymer 100 having reactive pendant moieties. Thebase polymer 100 is modified in accordance with a preferred embodimentof the present invention by forming a cross-linked skin 102 onto asurface thereof.

The base polymer 100 is preferably supported onto a substrate or support104, typically a non-woven or woven textile substrate. Base polymer 100is preferably covalently bound to substrate 104. Such covalent bindingbetween all structural components imparts extremely high chemicalstability to the novel membrane in aggressive operating conditions suchas extreme pH levels, high concentrations of acids or caustics, presenceof organic solvents, pressure, temperature and oxidation stability.Alternatively, the membrane may also be free-standing.

Cross-linked skin 102 is formed on a surface of base polymer 100. Thesurface preferably includes a top surface of base polymer 100, and mayalso include other exposed surfaces of base polymer 100, such as exposedsurfaces of pores in the base polymer as seen in FIG. 1.

The membranes of one embodiment of the present invention are preferablymicrofiltration (MF) or ultrafiltration (UF) membranes, most preferablyUF membranes. In general, the term “microfiltration membranes” refers tomembranes with pores having an average diameter of greater than about0.1 microns. They are commonly used to filter out small particles from aliquid while allowing the passage of smaller components such asdissolved salts and organic species having a molecular weight of lessthan about 100,000.

Ultrafiltration membranes typically have pore sizes of from about 0.1micron to about 5 nanometers. UF membranes are commonly classified bytheir ability to retain specific-sized components dissolved in asolution. This is referred to as the molecular weight cut-off (MWCO). UFmembranes are commonly used to retain proteins, starches, and other highto medium molecular weight dissolved species, while allowing thepermeation of simple salts and smaller dissolved organic compounds.

Usually MF and UF membranes are cast from solutions of polymers inselected organic solvents and have an asymmetric structure, as seen inFIG. 1. This means that the porosity of the base polymer varies from atop layer 106, having relatively small pores, to the bottom of the basepolymer having relatively large pores. This structure offers an optimalcombination of mechanical stability and resistance to compaction underhydrostatic pressure and minimal resistance to flow passage, where therelatively thin top layer 106 having the smallest pores impartsselectivity to the membrane. The operating pressure used in MF or UFapplications is usually 0.1-5 atmospheres.

Base polymer 100 is preferably chosen from acrylonitrile homo-, co- andtri-polymers, polyamides (aliphatic and aromatic), polyvinyl chlorideand its copolymers, chlorinated polyvinyl chloride, cellulosics, epoxyresins (e.g. polyphenoxy), polyarylene oxides, polycarbonates, homo- andco-polymers on the basis of heterocyclic compounds, (e.g.polybenzimidazoles), polyvinylidene fluoride, polytetrafluoroethylene,polyesters (saturated and non saturated which may be cross-linkedthrough the double bonds after membrane formation), polyimides,fluoropolymers, polysulfones, polyether sulfones, polyaryl sulfones,polyetherketones, polyether etherketones, polyelectrolyte complexes,polyolefins, polyphenylene sulfide, and polyphenoxy polymers, andderivatives of the above listed polymers which can be made intoasymmetric membranes. Such derivatives are generally but not exclusivelybased on sulfonation, nitration and amination, carboxylation,hydroxylation, nitrilation, halogenation (e.g. bromination), hydroxymethylated, ethers and esters of hydroxylated derivatives, and partialhydrolysis to increase the number of end groups. Asymmetric membranesmay also be made from a mixture of more than one polymer, e.g.,polyvinylidene fluoride and polyvinyl acetate.

Derivatives of engineering plastics, some of which have been mentionedabove, dissolved in appropriate solvents may also be used as basepolymer 100. Examples of such engineering polymers are polysulfones,polyethersulfones, polyphenysulfones, polyetherketones,polyetheretherketones, aromatic polyamideimide, polyimides,+polyphenylene oxides, polybenzimidazoles, aromatic polyamides,phenoxypolymers, fluoropolymers such as polyvinylidene fluoride and itscopolymers, polyolefins such as polyethylene and polypropylene and theircopolymers, polyvinyl chloride and its copolymers, polystyrene and itsco and tri polymers, polyacrylonitile and co and tri polymers, etc.

In order to form cross-linked skin 102, base polymer 100 must havereactive pendant groups. While the pendant groups can comprise anyreactive moiety, preferred groups are halogen and nitrile groups.

In some embodiments, the pendant groups are intrinsic to base polymer100. Especially preferred polymers are polyacrylonitrile, polyvinylidenefluoride, and copolymers thereof. Polyacrylonitrile is most especiallypreferred.

In other embodiments, the reactive pendant groups are added to the outersurface of base polymer 100 by a chemical process. Polysulfone,polyether sulfone and polyphenylene sulfone are known to have very goodstability in concentrated acids and bases, and are resistant tooxidizing media, and are thus preferred polymers to be used as basepolymer 100. Polyether sulfone is especially preferred. However, sincethey do not have reactive functional groups, it is necessary to carryout a pretreatment step in which reactive functional groups are attachedto or grafted onto the porous surface of the membranes.

Some non-limiting examples of chemical reactions that can introduce suchfunctional groups are:

(1) Oxidation of the surface with oxidants such as ozone or ammoniumpersulfate, followed by a reaction with multifunctional reagents such asa derivative of cyanuric chloride, for example, whereby the membranebecomes amenable to a subsequent step of cross-linking with high MW PEI(mentioned above).

(2) Plasma oxidation of the top layer, whereby —OH and —OOH groups,which can be subsequently reacted with a variety of amine and hydroxylreactants, are introduced into the surface.

(3) Formation of diazonium groups onto aryl polymers according to amethod described in U.S. Pat. No. 5,024,765, incorporated herein byreference.

(4) Radical grafting of vinyl moieties which can be subsequently boundto a cross-linking polymer such PEI or PVA.

(5) Other methods of introducing a variety of functional groups ontopolysulfones mentioned in the literature, such as carboxylation,sulfonation or electrophilic aromatic substitution sulfonation, such asmentioned in A. Noshay and L. M. Robertson, J. Appl. Polym, Sci., 20, p.1885 (1976); halomethylation as mentioned in A. Warshaysky et al, J.Polym. Sci. Part A: Polym. Chem., 28, p. 2885 (1990); nitration,amination and bromination as mentioned in M. D. Guiver, O. Kutowy and J.W. A. Simon, Polymer, 30, p. 1137 (1989); chlorosulfonation as mentionedin Quing Shi et al. J. of Membrane Sci. 319 p. 271 (2008). All these areincorporated herein by reference.

Pendant groups in such functionalize polymers may be, for example,sulfonic, chlorosulfonic groups, carboxylic, nitro, hydroxyl,hydroxymethyl, esters and ethers of the hydroxymethyl and hydroxyalkyland hydroxyaromatic groups and their ester and ether derivatives,halomethyl groups, sulfide, and thioalkyl and thioaromatic, vinyl,allylic, acetylenic, phosphine, phosphonicand phosphinic, aminomethylated etc. The substituted polysulfone membranes described in U.S.Pat. No. 4,894,159, U.S. Pat. No. 4,517,353, and A. Warshawsky et al.,J. of Polymer Sci., Part A: Polymer Chemistry, Vol. 28, 3303-3315 (1990)all incorporated by reference herein. An attractive way of derivingaromatic polymers, especially polysulfone polymers is by thehalomethylation and subsequent derivatization as described in theWarshawsky reference.

Cross-linked skin 102 is formed by reacting an oligomer or polymer,preferably a polymer, with the reactive pendant groups on the surface ofbase polymer 100. The oligomer or polymer can be any compound that canreact with the reactive pendant moieties on the base polymer.Advantageously, the oligomer or polymer has groups selected from primaryamino, secondary amino and hydroxyl groups. Polyethylenimine andpolyvinylalcohol are preferred polymers, and polyethylenimine isespecially preferred.

Due to the convenience of working with aqueous solutions, the polymerused to form cross-linked skin 102 is preferably a hydrophilic polymer.However, it will be appreciated that cross-linked skin 102 can also beformed using a hydrophobic polymer, so long as the hydrophobic polymercan react with the reactive pendant groups of base polymer 100.

Reference is now made to FIG. 2A, which is a computer-enhancedphotomicrograph of one example of the ultrafiltration membrane ofFIG. 1. The membrane shown in FIG. 2A comprises polyacrylonitrile as thebase polymer supported on a non-woven textile substrate (not shown). Thecross-linked skin is formed by reaction of polyethylenimine with thepolyacrylonitrile base polymer.

Reference is now made to FIG. 2B, which is a computer-enhancedphotomicrograph of another example of the ultrafiltration membrane ofFIG. 1. This membrane comprises polyether sulfone as the base polymersupported on a non-woven textile substrate. It is seen in FIG. 2B thatthe membrane is asymmetric, with pore size increasing from the top ofthe membrane to the bottom.

Examples of commercially available membrane products include AbcorHFK-131 MWCO 10K, Osmonics Sepa HZ-03 (MWCO 40 to 50K) and Sepa HZ-05(MWCO 2K), Desal E-100 (MWCO 35K) and E-500 (MWCO 500,00), Filtron Omega300K, 30K and 10K, and UF and MF membranes from Sepro, Nadir, GE, PCI,and X-Flow and Koch.

The membranes are commercially available in various configurations forvarious applications. Such membrane configurations include, inter alia,flat sheets, tubular, tubelets and hollow fibers. The tubes and flatsheets are preferably supported on woven and more preferably non-wovenmaterial but the tubelets and hollow fibers are generally not supported.The non-woven or woven materials may be made of polyolefins (e.g.polypropylene or polypropylene/polyethylene, polyesters, polyimides,polyamides, polyether ketones, polysulfides and inorganics or glass ormetal materials.

Prior art membranes are configured in a modular form of spirals orplates and frames or hollow fibers, or tubular systems. A list ofmanufacturers of asymmetric porous membranes and modules, for all thedifferent configurations, made of organic polymers, ceramics andinorganic may be found in e.g. “Handbook of Industrial Membranes”, K.Scott, Elsevier Publishers, section 2.1, p. 187-269; “Basic principlesof membrane technology”, M. Mulder, p. 465-473 (1996); “Membranes forindustrial wastewater recovery and reuse”, Simon Judd & Bruce Jefferson(eds), Elsevier, Chapter 2 (2003).

Reference is now made to FIGS. 3A and 3B, which are simplifiedillustrations of chemical reactions which take place in the manufactureof the ultrafiltration membrane of FIG. 1 in accordance with embodimentsof the present invention and which produce covalent bonding between basepolymer 100 and cross-linked skin 102.

The reaction is preferably initiated by immersing the membrane (made ofpolyacrylonitrile) into a solution of a polymer with which it can react(polyethylenimine). The reaction is preferably carried out at elevatedtemperature, usually in the range 50-100° C., preferably in the range70-90° C. Reaction time is 1 to 72 hours, preferably 5 to 32 hours, morepreferably 10 to 20 hours.

The polyethylenimine (PEI) solution has a concentration between 2%-10%(preferably 4%) in water. Molecular weight of PEI is high (between20,000 to 750,000), however polymers, oligomers and even small organicamines can be also used according to a method of the invention; ineffect the molecular weight range can cover the whole range from 400-1million, but preferably the molecular weight is between 800-20,000.

Optionally, the reaction may be followed by a step of drying at elevatedtemperature, usually in the range 70-120° C., preferably in the range80-100° C., most preferably in the range 90-95° C., and desirably usingpreheated air or other gas at such temperatures. A preferred time forthe drying step is 1-3 hours.

The drying step is important since according to the invention thesurface concentration of the amine containing surface increases,chemically modifying the surface and achieving a high surface density ofcross-links. After this step the membrane is solvent stable and can beimmersed in almost any solvent without being destroyed. Optionally, thebulk of the PEI layer that has been chemically attached to the PANsurface is subsequently reacted with a cross-linking species dissolvedin aqueous solution. Then the membrane is dried for 1-3 hours at 40-60°C. It is then washed with distilled water and thereafter it is ready toserve as a UF support membrane for various types of membranes, such as,inter alia, NF, RO and PV.

In a different embodiment, the reaction takes place at room temperature.However, the result is a skin with a low degree of cross-linking (FIG.3A) as opposed to the high degree of cross-linking achieved by thereaction at 90° C. (FIG. 3B). The degree of cross-linking is alsoaffected by reaction time, drying conditions, and the molecular weightand concentration of the skin polymer, etc.

In addition to surface modification methods employing the mentionedpolyamines, the surface modification method can be carried out usingother types of polymers and oligomers, such as polyvinyl amines, aminoderivatives of styrene and its copolymers, and polyvinyl alcohol and itsderivatives. Derivatives of these polyamines can contain sulfonic,carboxylic and phosphonium groups to make charged and amphotericmonomeric, oligomeric and polymeric molecules, as described in the abovepatents, including U.S. Pat. No. 4,659,474, and copolymers which containdifferent groups, especially polar and ionic groups. As described in theabove patents, the polyamines may also be taken for example from thecategory of polyvinylamines and their co- and tri-polymers, polyaromaticcompounds such as aminopolystyrene, amine-containing engineeringplastics of aromatic polysulfones, polyethylenimines and derivatives ofpolyethylenimine.

In addition there are polyphenol polymers such as polyvinylphenol andits copolymers. These polymers are reactive, not only through their —OHgroups but also because they have activated or electron rich aromaticstructures which may readily undergo electrophilic reactions withelectrophiles such as formaldehyde or other aldehydes. Besides phenolicgroups on a polymer chain, there may also be aryl amines which are alsoreactive because of both the amino groups, and the electron richaromatic groups. Similar systems based on thiophenols are also included.

The reaction of vinyl pyridines and a dihalo organic compound forms across-linked insoluble copolymer, and may undergo subsequent reaction aswith amines. These reactive combinations as described in U.S. Pat. No.4,014,798, incorporated herein by reference, can be used to modify thesurface layers in embodiments of the invention. The reaction between di-or poly-halogenated (especially chloro- and bromo-) alkyl and benzylorganics with polyfunctional amines and hydroxy compounds and oligomersand low molecular weight compounds are additional preferred reactions.

Cationic and anionic polymerization and condensation polymerizationsystems may also be used to modify the surface layers. Appropriatepolymerization chemicals and procedures are known.

As will readily be appreciated, where possible, water is the preferredmedium for many important membrane formation procedures of theinvention. It is inexpensive, safe to handle and has good solubilityproperties especially when the components are in low concentration. Theuse of aqueous solvents determines the type of reactants that will beused and how they are applied. If polymeric components and reactants donot have the needed degree of solubility in water, then solvents canoften be added to improve the solubility in water. Appropriate watermiscible solvents include acetone, methanol, ethanol isopropanol, DMF,NMP, DMSO, THF, sulfoxane, etc., provided that their addition is atsufficiently low concentrations and will not damage the porous membranestructure or its properties. In addition the surface cross-linkingmethod can be performed by means of hydrophobic reactive polymers thatcan be dissolved in organic solvents which do not damage the UF/MFmembranes.

It is appreciated that polymers other than water soluble polymers may beemployed. For example, polymers which are present in aqueous solution asaqueous dispersions, such as emulsions or suspensions, may also be used.

Reference is now made to FIGS. 4A and 4B, which are simplifiedillustrations of chemical reactions which take place in the manufactureof the ultrafiltration membrane of FIG. 1 in accordance with anotherembodiment of the present invention. In this embodiment, base polymer100 comprises polyvinylidene fluoride (PVDF) instead of PAN.

In the case of PAN and PVDF membranes, a direct reaction with PEI, forexample, occurs on the surface forming a chemically bound andstabilized, surface cross-linked membrane with unique stability inorganic solvents. This is a surprising outcome, since, according to theprior art, in order to achieve solvent stable membranes, thecross-linking reaction must occur in the entire bulk of the polymericmembrane. The prior art suggests that only low MW reactants acting inpresence of swelling agents could cross-link the entire membrane matrix.However, surprisingly, in accordance with the present invention, the useof high molecular PEI chemically reacted with the surface of a porous UFor MF membrane, is sufficient to impart to such treated membraneoutstanding stability to a great many organic solvents.

It will be appreciated that the present invention provides a significantadvantage promising significant savings in manufacturing chemicallystable membranes by using commercially available polymers, castingformulations and membranes. For example, by using this novel fabricationmethodology it is possible to take a commercially available UF or MFmembrane made from PAN or PVDF and by using the existing functionalgroups on the membrane surface, to convert such membranes to highlysolvent resistant UF/MF membranes by reacting them on a surface with apolymeric reactant.

After achieving solvent stability in this manner, the modified membranecan be exposed to many additional reactions if required. Such additionof functionality sometimes requires rigorous reaction conditions inorganic solvents and could not have been performed effectively withoutcausing structural and functional damage to the porous membrane, priorto obtaining the modified membrane in accordance with embodiments of thepresent invention. A more detailed description is given below.

The membrane may be treated, prior to operating in accordance with themethod of the invention, by well known, state-of-the-art methods, suchas cleaning with surfactants, use of surfactants to modify wettingproperties, annealing by heat treatment to change pore size, and/orpre-wetting with solvents to which such membranes are stable.

According to the approach disclosed herein, a polymeric asymmetric orporous UF/MF membrane that already has good chemical stability in someenvironments may be selected, and by modification, good stability inorganic solvents may be imparted thereto. As a result of this approach,the general stability of such surface cross-linked membranes issignificantly improved. For example, not only the solvent stability ofPAN is improved but also its stability with respect to concentratedacids. Whereas unmodified PAN membranes disintegrate after a shortperiod of time in 20% sulfuric acid at 90° C., and would be dissolved bymany organic solvents, after processing such membranes in accordancewith the methodology of an embodiment of the invention, modified PANmembranes that have a combination of good solvent stability, compactionstability and stability in hot sulfuric acid are obtained.

The methodology may be adopted for achieving polymeric membranes thathave enhanced stability in complex environments, combining resistance toattack by organic solvents and by aggressive chemical conditions such asextreme pH, aggressive oxidizing environments and the like. A polymericUF membrane support that is known to have stability in certainaggressive environments may be selected and modified by covalentattachment to a surface of a UF/MF support so that after the covalentattachment modification step, the membrane possesses additionalstability against attack by organic solvents. For example PVDF is knownto possess good stability in an acidic environment, and, by modifying bycovalent attachment such PVDF membranes, a combination of acid andsolvent stability is obtained.

The preferred use of PEI in the present invention is based on itsbi-or-multi-functional character, whereby it may perform multifunctionalattachment to, e.g. PAN, PVDF and other derivatized membranes, bycross-linking to the surface, thereby modifying the surface and creatinga reactive layer at the surface of UF/MF membranes, rendering themreactive with subsequent layers.

When the membrane material does not have reactive groups, it is possibleto graft chemical functional groups onto the surface of the UF/MFmembrane under mild reaction conditions and then subsequently to react apolymeric reactant with this modified membrane also under mild reactionconditions without causing any damage to the membrane. In this manner,such modified membranes are imparted with excellent solvent stability.For example PES (polyether sulfone) membranes that are known to havegood acid, base and oxidizing stability can be reacted on their surfaceswith a polymeric reactant to generate unique chemically stable membraneswith unusual +combinations of properties such as solvent, acid base andoxidation resistances, for example.

Often UF membranes serve as substrates for producing a tighter class ofmembranes such as pervaporation (PV), nanofiltration (NF) and reverseosmosis (RO) membranes, where a top PV or NF or RO layer that is facinga liquid being treated is located on the UF support. The NF & ROapplications are used at much higher pressures than those used in the MFor UF applications. Typical operating pressures are in the range of10-40 bars in the NF applications and 20-100 bars in the ROapplications. As a result, compaction of UF supports and mechanicaldeformations may occur and cause damage to the connection between thedifferent parts of the membrane (non-woven support, UF membranes and thetop NF or RO layers).

Reference is now made to FIG. 5, which is a simplified illustration of ananofiltration membrane constructed and operative in accordance with anembodiment of the present invention. As illustrated in FIG. 5, there isprovided a polymeric nanofiltration membrane including anon-cross-linked base polymer 100 having reactive pendant moieties. Thebase polymer 100 is modified by forming a cross-linked skin 102 onto asurface thereof. A nanofiltration layer 108 is formed on the top surfaceof cross-linked skin 102. Base polymer 100 and cross-linked skin 102 arepreferably as described hereinabove with reference to FIGS. 1-4B.

Nanofiltration layer 108 comprises at least one di-, tri- or tetra-halosubstituted diazine or triazine-containing monomer, oligomer or polymer,and at least one multifunctional amine having a molecular weight in therange of 400 to 750,000, provided that at least one of the di-, tri- ortetra-halo substituted diazine or triazine-containing monomer, oligomeror polymer is not a di- or triazine monomer which is substituted only byCl. Nanofiltration layer 108 optionally comprises at least onesupplemental cross-linker.

In some embodiments, the di-, tri- or tetra-halo substituted diazine ortriazine-containing monomer or oligomer is selected from the groupconsisting of:

wherein:R¹ is independently selected at each occurrence from bromo, chloro,iodo, fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selectedat each occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R² is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R³ is independently selected at each occurrence from bromo, chloro,fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independently selected ateach occurrence from H, optionally substituted alkyl and optionallysubstituted aryl;R⁴ is selected from H, bromo, chloro, fluoro, —NHR⁵, —OR⁵ and SR⁵,whereinR⁵ is independently selected at each occurrence from H, optionallysubstituted alkyl and optionally substituted aryl; andR⁸ is independently selected at each occurrence from —NH₂— and—NH-A-NH—, wherein A is selected from C₁₋₂₀ aliphatic moieties, C₆₋₁₀aromatic moieties, and combinations thereof;

provided that at at least two occurrences, R¹, R², R³ and R⁴, takentogether, are selected from bromo, chloro and fluoro, and furtherprovided that when both R¹ and R² on a single ring are Cl, at least oneof R³ and R⁴ is not Cl.

In some embodiments, the multifunctional amine is selected from thegroup consisting of polyethylenemine, polyvinylamine, polyvinylanilines,polybenzylamines, polyvinylimidazolines, and amine-modifiedpolyepihalohydrins. Polyethylenimine is especially preferred.

In some embodiments, the supplemental cross-linker is selected from thegroup consisting of 2,4,6-trichloro-s-triazine, 4,6-dichloro-2-sodiump-sulfoanile-s-triazine (4,6-dichloro-2-p-anilinesulfonic acid sodiumsalt-s-triazine), 4,6-dichloro-2-diethanolamine-s-triazine and4,6-dichloro-2-amino-s-triazine. In some embodiments, the matrixcomprises cationic functional groups.

When the di-, tri- or tetra-halo substituted diazine- ortriazine-containing compounds that are utilized to make thenanofiltration layers that are used in accordance with embodiments ofthe present invention are in the form of oligomers or polymers, theindividual diazine or triazine units may be bonded by linkages whichconsist primarily of aliphatic, aromatic or mixed aliphatic/aromatichydrocarbon fragments, e.g. one or more straight or branched C₁₋₂₀aliphatic units which may also bonded to one or more C₆₋₁₀ aromaticunits. These linkages may further contain, and be bonded directly to,the diazine or triazine portions, by amine linkages, i.e. via C—N bonds.Such linkages may also be —NH— linkages. It will be appreciated that notall the linkages in the polymers used in embodiments of the inventionneed be acid stable, provided that the percent of such non-acid stablelinkages is sufficiently small that membrane performance will still beacceptable.

In the context of this application, the term “multifunctional amine”refers to a compound having at least one primary or secondary aminemoiety and at least one other functional group, such as —COOH, ester,amide, ketone, aldehyde, tertiary or quaternary amine and the like. Insome embodiments, the multifunctional amine contains a first primary orsecondary amine near one terminus of the molecule and a second primaryor secondary amine near another terminus of the molecule. In someembodiments the multifunctional amine contains multiple primary orsecondary amine moieties spaced intermittently through the molecule.

It will be appreciated that the multifunctional amines used in producingthe NF membranes used in accordance with embodiments of the inventiongenerally have one or more carbon chains (in which some carbon atoms mayoptionally be replaced with O or N) and/or carbon rings, such as phenylrings, so that the multifunctional amines will have molecular weightsranging from 400 to 750,000. The multifunctional amines may thus beoligomeric or polymeric compounds having both amine functionality aswell other functionality, which may appear at regular or semi-regularintervals, although they may also be monomeric (preferably having atleast two separate amine moieties on the monomeric molecule), providedthat they may cross-link with at least two of the halo-substituteddiazine or triazine moieties.

The multifunctional amines used to make polymer nanofiltration layersfor use in embodiments of the invention may be amine compound residuesderived from an amine compound having any organic nucleus and at leasttwo primary and/or secondary amine groups. In some embodiments, theamine compound has the formula R¹¹—NH—Y—[(CH₂)_(j)(NHR¹²)]_(m) whereinR¹¹ and R¹² are independently hydrogen or aliphatic groups of 1 to 30carbons; Y is any appropriate organic moiety, e.g. of 1 to 30 carbons,and optionally containing one or more oxygen, sulfur or nitrogen atoms,such as an aliphatic, aryl or arylalkyl group of 1 to 30 carbons or acorresponding heteroaliphatic, heteroaryl or heteroarylalkyl groupcontaining one or more oxygen, sulfur or nitrogen atoms; m is an integerfrom 1 to 3; and j is an integer of from 0 to about 10.

The functional groups present in the multifunctional amine may be chosento help impart desired properties to the resulting NF membrane. Thus, inprinciple, functional groups may, for example, be ionizable groups,non-ionizable hydrophobic groups, or non-ionic hydrophilic groups. Insome embodiments, the resulting NF membranes will contain cationicfunctional groups, as it is believed that the presence of such groupswill increase the retention of copper ions. In the context of thepresent application, the term “cationic functional group” refers to bothfunctional groups which are cationic at virtually all pH values (e.g.quaternary amines) as well as functional groups that can become cationicunder acidic conditions and/or can become cationic through chemicalconversion (e.g. primary and secondary amines or amides).

Similarly, the degree of cross-linking within the matrix will influencethe properties of the NF membrane. The degree of cross-linking, which isexpressed as a percentage, is defined as the number of moles of moietieswhich actually cross-link out of the total number of moieties availableto cross-link. In some embodiments, the degree of cross-linking is from2% to 45% mol/mol. In some embodiments, the degree of cross-linking isfrom 8 to 25% mol/mol. In some embodiments, the degree of cross-linkingis from 9 to 15% mol/mol.

It will also be appreciated that in some embodiments, themultifunctional amines may themselves contain the halo-substituted di-and/or triazine moieties, in which case the multifunctional amines maymade to self-react to form the matrix.

FIG. 6 is a computer-enhanced photomicrograph of one example of thenanofiltration membrane of FIG. 5. The membrane shown in FIG. 6comprises polyacrylonitrile as the base polymer, a cross-linked skinformed by reaction of polyethylenimine with the polyacrylonitrile basepolymer, and a nanofiltration layer A made of polyethylenimine andtriazine. It is appreciated that the nanofiltration layer A is thinnerand denser than the ultrafiltration layer over which it is formed.

In order to enable permeation of a fluid through a membrane, thereshould exist a plurality of pores, void spaces, or free volumes withinthe membrane which can act as conduits through which the fluidpermeates. Such conduits may exist permanently within the film, or mayexist transiently as with polymer dynamic fluctuations. They may becontinuously connected, or they may be temporarily connected as aconsequence of the random movements of the various polymer chains in themembrane. Both the size and number of these free volume regions governthe permeability of a membrane, with an increase in either leading tohigher permeability. The size of these free volume regions is, however,limited by the need to retain solutes such as dissolved metal ions,cations, or organic compounds.

Typically, to prevent the membrane from transmitting solutes, themembrane should not contain a high proportion of continuous spaces,i.e., pores, void spaces, or free volume areas through which the solutescan pass without significant restriction. Large void spaces can allowfeed solution to pass the membrane without significant retention of thedesired solutes. In practice, such voids present in RO and NF membranesare often referred to as defects. The presence of defects does notnecessarily render a membrane unusable in accordance with embodiments ofthe present invention, as long as there are sufficiently few defects toallow the membrane to meet its specified performance criteria.

The thickness of the nanofiltration layer also affects performance.Generally, a thicker separating layer offers greater resistance to flowand, thus, will require a higher driving force to produce a flow similarto that of a thinner membrane. For this reason, it is preferred that thethickness of the nanofiltration layer of these membranes be less thanabout 1 micron, more preferably less than about 0.5 microns and mostpreferably less than about 0.1 micron. However, a common feature of thinfilms is an increased tendency to exhibit defects as thicknessdecreases. These defects can arise from one or more of a variety offactors. In general, they are associated with a loss in mechanicalintegrity as the film becomes progressively thinner. For example, whenthe mechanical integrity of such a film is compromised, the chance thatapplied pressures may violate the integrity of the film increases. Forthese reasons it has been found that it is often useful for thenanofiltration layers to be thicker than at least about 0.005 microns,and more preferably thicker than about 0.02 microns.

It will be appreciated that when monolithic membrane structures, i.e.those in which the NF layer is covalently bound to the underlyingsupport membrane, are utilized as in accordance with embodiments of thepresent invention, layers that are thinner than those used when the NFlayer is not covalently bound to the underlying support membrane can beemployed.

FIGS. 7A and 7B are simplified illustrations of chemical reactions whichtake place in the manufacture of the nanofiltration membrane of FIG. 5in accordance with one embodiment of the present invention and whichproduce covalent bonding between cross-linked skin 102 andnanofiltration layer 108.

In some embodiments, the matrix is formed by a process which comprisesproviding an asymmetric base ultrafiltration membrane which at one facethereof has pores of smaller diameter than at the opposite face;providing a solution containing at least one di- or tri-halo substituteddiazine or triazine-containing monomer or oligomer, at least onemultifunctional amine having a molecular weight in the range of 400 to750,000, and optionally, at least one supplemental cross-linker; andbringing the solution into contact with the face of the ultrafiltrationmembrane having smaller pores under superatmospheric pressure for a timesufficient to effect covalent bonding of the at least one di- ortri-halo substituted diazine or triazine-containing monomer or oligomerand the at least one multi-functional amine.

In some embodiments, the time and pressure are sufficient to effectcovalent bonding at of the least one di- or tri-halo substituted diazineor triazine-containing monomer or oligomer, the at least onemulti-functional amine, and the surface of the pores of theultrafiltration membrane. In some embodiments, prior to the contacting,the ultrafiltration membrane has been modified to facilitate covalentbonding to the surface thereof. In some embodiments, the formation ofthe nanofiltration membrane further comprises, after the contacting,heating the ultrafiltration membrane.

The matrix layer may also be covalently bound to the underlying UF or MFsupport by other attachment methods, such as by a direct chemicalreaction not involving an application of hydrostatic pressure or vacuum,dip coating methods and coating of the UF support (e.g. by gravurecoating, knife coating or air knife coating) following by formation of amatrix layer in a manner that results in covalent binding to a UF or MFsupport membrane.

When the multifunctional amine is a polymer or oligomer, and/or thehalogenated di- and/or triazines are present as part of a polymer oroligomer, the polymers or oligomers may include functional groups aspart of the polymer/oligomer chain, e.g., a polyamine oligomer, or thesegroups can be attached as pendant groups. These groups can beincorporated into the polymer by any suitable route. A particularlyefficient method is to use a multifunctional monomer with the desiredfunctionality, or a derivative of the functionality, incorporated withinthe structure. Appropriately prepared polymers incorporating suchmonomers would have the desired functionality throughout the membranematrix.

It has been found that a condensate formed from cyanuric chloride andsulfanilic acid, a synthesis of which is described below, is a suitablehalogenated triazine for use in preparing membranes for use inaccordance with embodiments of the present invention.

Non-limiting examples of a functional group that are cationic at all pHranges are quarternary ammonium groups. Primary, secondary and tertiaryammonium groups are examples of groups that become cationic at certainpH levels. Another type of a “cationic functional group” is one which isgenerated by a chemical reaction. It will be clear to those skilled inthe art that the phrase “potentially cationic” refers simply to chemicalfunctional groups which are cationic or could become cationic based onpH and/or chemical conversion.

It will be appreciated that the nanofiltration layer need notnecessarily contain an excess of cationic functionality. If thenanofiltration layer can be prepared with sufficiently designedseparation channels, a separation can be attained mainly through sizeexclusion. However, it is believed that in most instances, suitablemembranes will possess cationic or potentially cationic groups whichassist the separation through charge-charge interactions.

In some embodiments the polymer, such as an amine-containing polymer ortrazinic polymer, contains mixed charged groups, such as a mixture ofcation exchange groups (e.g. sulfonic or carboxylic) and anion exchangegroups (e.g. quaternary ammonium groups). Such mixed charges can bedistributed homogenously through the matrix or separated into domains,for example by using block copolymers to prepare the matrix, whereinseparate blocks of the block copolymer have a cationic or anioniccharacter.

In an example shown in FIG. 7A, base polymer 100 is polyvinylidenefluoride. Cross-linked skin 102 is formed by reacting polyethyleniminewith the polyvinylide fluoride. Nanofiltration layer 108 is formed byreacting polyethylenimine and a halo-substituted triazine compound withthe cross-linked skin. FIG. 7B is similar to FIG. 7A except that in FIG.7B, base polymer 100 is polyacrylonitrile.

In order to evaluate the long-term stability of the membrane in acids, asuitable method is to use temperature to accelerate degradation. As areasonable approximation, the rate of many such degradation reactions isdoubled with every 10° C. increase in temperature. Thus a thirty-dayexposure to an acid at 40° C. can be approximated with a 24 hourexposure at 90° C. Of course the high temperature method is not possiblefor membranes including heat sensitive polymers or other membranes wherewhose membrane degradation is not temperature dependent in the mannerdescribed above. In such cases, a lower temperature, longer exposuretest is required to gauge acid stability.

It is not the intent of this disclosure to exclude such heat sensitivepolymers, rather, to provide an acid stable membrane and a test forgauging acid stability. For purposes of the present patent application,it will be appreciated that membranes assessed on the basis ofperformance need only meet one of the three recited performancecriteria, namely, for example, exposure of the nanofiltration membraneto either (i) 75% sulfuric acid at 60° C. for 300 hours, (ii) 20%sulfuric acid at 90° C. for 180 hours, or (iii) 20% sulfuric acid at 45°C. for 60 days, the nanofiltration membrane removes at least 70% of thecopper ions at a flux greater than 1 gfd from a feed solution of 8.5%CuSO₄ in 20% sulfuric acid when the feed solution is applied to themembrane at a feed pressure of 600 psig and a temperature of 25° C.

The present invention provides improved membranes that show desirablestability and performance under a variety of conditions, includingpresence of organic solvents and strong acids. The improved membranesare formed by the reaction of reactive groups on the surface of acommercial membrane with a polymeric reactant.

Improvements in the water, chemical, food, energy and pharmaceuticalindustries often require developing and improving production processesto lower raw material and energy consumption, to minimize wastage andthe resultant environmental damage, and to recover waste materials,water and solvents. Membrane separations are becoming increasinglyimportant in this worldwide effort. For many applications, however, theexisting membranes are still not sufficiently selective and/or stable.There are many examples of industrial applications that could benefitfrom the advantages of membrane technology, provided that membranespossessing the proper and diverse combination of stability andselectivity are available. However the required combination of suchseparation and stability characteristics is often lacking.

The following are examples of some of the required properties formembranes required by industry but not available:

(i) the combination of acid stability (20-90% acid concentrations) andsolvent stability is required for removing organic solvents fromconcentrated mineral acids;

(ii) the combination of stability in organic solvents with stability inhigh alkaline conditions is required for separations in pharmaceutical,chemical and metal industries;

(iii) compaction stability under high applied hydrostatic pressures atelevated temperatures, and sometimes in the presence of organic solventsis required for performing separations in many types of industrialwastewater streams;

(iv) separating soluble catalysts from organic solvent streams inextreme pH conditions and in oxidizing or highly reactive environmentsrequire appropriately stable membranes.

One objective of the present invention is to provide a method forconverting almost any polymeric asymmetric MF and/or UF support membraneinto a surface cross-linked, chemically and solvent stable membrane thatis fully integral, mechanically stable and having on the surfaces ofeach layer of the membrane, functional groups that are capable of beingchemically bound to any of the adjacent layers, thereby forming amonolithic robust structure.

It will be appreciated that many separation processes may benefit fromimprovements to membrane technology in accordance with the presentinvention. Process simplicity, energy saving, economic advantage, thepossibility to recover and recycle raw materials, such as water, acids,bases and solvents are enhanced as a result of the provision ofchemically stable support membranes in accordance with embodiments ofthe present invention.

In general, a modified non cross-linked polymeric semipermeable membraneis characterized by having improved stability compared to the nonmodified membrane in an aggressive environment characterized by at leastone of the following: acid media, basic media, oxidizing species,elevated temperatures and elevated pressure.

Embodiments of the present invention relate to a method for surfacecross-linking micro-porous UF or MF membranes or membrane supports,containing on the surfaces of the porous membrane structure, functionalgroups that can chemically attach to a polymer being reacted with suchsurfaces from a solution contacting the membrane surfaces, therebyconverting such treated porous membrane/membrane supports to surfacecross-linked, chemically stable and solvent stable membranes.

In another aspect, embodiments of the present invention provide a methodfor introducing chemically reactive groups, capable of subsequentchemical binding to polymers dissolved in a solution in contact with themembrane surfaces, to the surfaces of porous membranes not containingsuch reactive groups initially.

In yet another aspect, embodiments of the present invention providemethods for binding porous membranes/membrane supports to an underlyingsubstrate such as non-woven or woven material, thereby forming amonolithic stable membrane UF/MF structure.

In still another aspect, embodiments of the present invention providebound polymers on the surfaces of the UF/MF micro-porous membranes thatare capable of reacting and forming chemical bonds with a subsequentlyoverlaying top layer of NF, RO, PV thin film membrane, thus forming amonolithic membrane structure in which the top layer is chemically boundto the underlying support structure. The cases where functional groups,capable of chemically binding with a top layer, already exist on theMF/UF membrane originally, are also included within the scope of theinvention.

In general terms, the present invention relates to ultra-filtration (UF)and microfiltration (MF) membranes with improved solvent and chemicalresistance, where the term ‘chemical resistance’ may imply any or all ofacid, base, oxidant, thermal and compaction resistance. Such membranescan be manufactured from practically any existing membrane usingvirtually any type of polymer described above, including, inter alia,homo- or copolymers such as acrylonitrile, vinylidene aromatic polymers(PS, PES, PPSu), aliphatic polymers.

Moreover, embodiments of the present invention are directed to processesand to membranes made by such processes, for surface cross-linkingasymmetric porous supports in MF or UF molecular weight cutoffs, thatcan also serve as membrane supports for the top layer comprising NF, RO,PV, MD and other types of selective barriers used in separation orconversion processes. The surface cross-linking property is achievedrapidly and efficiently, usually using aqueous treatment solutions andusing well-known and relatively inexpensive reactive polymers such asamine (e.g. PEI), alcohols and other polymers such as those mentionedabove.

One additional object of the present invention is to provide a methodfor manufacturing solvent and chemically resistant membranes made frompre-cast UF/MF membranes or other types of microporous membranes basedon e.g. polyarylsulfone polymers modified by chlorosulfonation in anorganic solvent that does not cause any damage to the membrane. Morespecifically the membranes may be modified by a chlorosulfonationreaction in glacial acetic acid or a mixture of acetic acid withnon-polar solvents such as CCl₄ and others.

The functional groups added to the surface of the UF/MF membrane may becapable of reacting on the surface with the reactive polymers. In caseswhere such direct binding reaction is not possible, for example when thegrafted groups are amines, alcohol or similar compounds, an intermediatemultifunctional group may be reacted with the activated surface makingit amenable to a reaction with a cross-linking polymer. Non-limitingexamples of multifunctional groups are: triazines, diazines, or theirderivatives. Instead of triazines or diazines, conditions may be foundfor the use of water soluble polyepoxides or an emulsion of waterinsoluble liquid epoxides, dihaloquinoxalines, polyaldehydes,polyisothiocyanates, polyalkyl halogens and polybenzyl halogens andother cross-linkers referred to above for reaction with reactive amino,hydroxy and sulfide containing polymers and oligomers, as well asdifferent types of silane derivatives.

In another preferred system polyhydroxy phenols or hydroxy benzenereagents or hydroxy or hydroxy methyl aromatic polymers such ashydroxymethyl polysulfones are reacted with the membrane usingpolyaldehydes or formaldehyde. In this case the reaction can proceedunder acidic or basic conditions. The conditions of reaction are readilydetermined.

WO 99/40996, the contents of which are incorporated herein by reference,discloses a method for making nanofiltration membranes by applyingsuperatmospheric pressure to force reactants in dilute solution into thesmaller pores of asymmetric base membranes. The reactants then react inthe pores to form a macromolecular structure within the pores and, ifthe reaction is allowed to continue for sufficient time, on the outersurface of the base membrane, thus forming a thin film on the basemembrane (i.e. a matrix), yielding a composite membrane. The reactantsare chosen so that the resulting film is a polymer film; if across-linker is included among the reactants, the polymer chains may becross-linked. Depending on the nature of the functional groups presentin the film, different properties may be imparted to the nanofiltrationmembrane.

WO 99/40996 does not disclose the use of di-, tri- or tetra-halosubstituted diazine or triazine-containing monomers, oligomers orpolymers, in which the monomer is not a di- or triazine having onlychloro substituents, as reactants. It has now been found that by usingsuch compounds, in combination with multifunctional amine compounds asreactants (which react with the diazine- and/or triazine-containingmonomers, oligomers and/or polymers to form a cross-linked matrix),optionally with additional cross-linkers, it is possible to obtaincomposite membranes that are stable to the acids used in copperseparation processes for long periods of time, retaining both their fluxand separation (selectivity), even at extremely low pH's. Use of thesemembranes in metal separation or recovery processes can thereforeimprove the efficiency of the separation or recovery processes of copperand other metals.

In particular, it has been found that after even after exposure of suchcomposite nanofiltration membranes to at least one of (i) 75% sulfuricacid at 60° C. for 300 hours, (ii) 20% sulfuric acid at 90° C. for 180hours, or (iii) 20% sulfuric acid at 45° C. for 60 days, thenanofiltration membranes remove at least 70% of the copper ions at aflux greater than 1 gfd from a feed solution of 8.5% CuSO₄ in 20%sulfuric acid when the feed solution is applied to the membrane at afeed pressure of 600 psig and a temperature of 25° C.

Similarly, WO 99/40996 does not disclose the stability achieved as aresult of covalently binding the NF matrix to the underlying UF support.Such membranes can be produced by using matrices and UF supports, asdescribed in co-pending U.S. provisional patent application No.61/193,962, and display the stability desired for use in copperseparation processes.

U.S. Pat. No. 4,659,474 discloses the formation of UF membranes bycoating on a porous polymeric substrate containing functional groups achemically reactive hydrophilic polymer from a dilute aqueous solutionunder pressure and cross-linking the polymer present on the poroussubstrate as a thin layer with low molecular weight polyfunctionalcompounds. The membranes obtained are not suitable for use as NFmembranes, as their pore sizes are too large.

In order to maintain the mechanical integrity of a thin film compositemembrane while in the presence of significant pressure differentials, itis common practice to provide a thicker porous membrane to act as asupport for the thin film (i.e. the matrix). Typically, these supportmaterials are 25 to 100 microns thick, although the actual thickness isnot critical, provided that it imparts the necessary mechanical supportat the required operating pressures. The supporting layer should provideminimal resistance to flux relative to that of the thin film. Suitablesupports are often found in ultra- or micro-filtration membranes. Thesemembranes have both good mechanical integrity and a nominal resistanceto flow relative to the thin films. Such supporting membranes are wellknown and can be prepared by numerous techniques such as phase inversionand track etching, among others. The material constituting thesemipermeable support is relatively unimportant so long as it is stableto the feed solution, pressure, and temperature, and so long as it iscompatible with the thin film. Non-limiting examples of materials whichmay be utilized to make the underlying supporting membrane includepolysulfones, polyethersulfones, polyvinylidene fluoride,polytetrafluoroethylene, polyvinylchloride, polystyrenes,polycarbonates, polyacrylonitriles, polyaramides, nylons, melamines,thermosetting polymers, polyketones (including polyether ketones andpolyetheretherketones), polyphenylenesulfide, ceramics, and porousglass. In some embodiments the supporting membranes are UF membraneswhich have been prepared as described in provisional U.S. ProvisionalPatent Application No. 61/193,962. In the case of polysulfones,polyethersulfones, polystyrenes, polyaramides, nylons, polyketones andpolyphenylenesulfides, prior to forming the NF matrix thereupon, it maybe desirable to modify the UF support by (a) forming a cross-linked UFlayer on the underlying UF support membrane, (b) introducing functionalgroups which can react with the multifunctional amine and thehalogenated di- or triazine compound, or both. U.S. Provisional PatentApplication No. 61/193,962 describes methods by which such modificationsmay be effected.

In some embodiments, the support material has an A value greater than 3l/(m²×h×bar), preferably greater than 5 l/(m²×h×bar) and more preferablygreater than 10 l/(m²×h×bar), provided that these values are obtained atan actual pressure at which the final NF membrane will operate. This isdue to the fact that A values of most ultrafiltration supports declineswhen a hydrostatic pressure is applied to them. In some embodiments thesupport material has an A value greater than 40 l/(m²×h×bar). In someembodiments the support material has an A value greater than 100l/(m²×h×bar). The A value of the support membrane should not declinebelow the A value of the matrix membrane under the applied hydrostaticpressure. In some embodiments, the A value of the support membrane is atleast 50% higher than the A value of the matrix itself. In someembodiments, the support material preferably has a molecular weight cutoff (measured by the ASTM method at 90% dextran rejection) of less than500,000. In some embodiments the molecular weight cut-off is less than100,000. In some embodiments the molecular weight cut-off is less than30,000. In some embodiments the molecular weight cut-off of the supportmaterial is less than 20,000.

As explained in WO 99/40996, the support material should have sufficientinitial permeability to the reactants to enable them to enter the poresof the support material under superatmospheric pressure. In someembodiments this initial permeability is at least 2%. In someembodiments it is at least 5%. In some embodiments it is at least 10%.In some embodiments it is at least 15%. In some embodiments it is atleast 20%.

Also as explained in WO 99/40996, it will be appreciated that thereactants in the dilute solution penetrate into the pores of theunderlying base membrane, where the reactants become sufficientlyconcentrated to react therein, whereas by contrast little or no reactiontakes place initially in the solution or on the outer surface of theunderlying support membrane. When reaction at the surface takes place,this will generally occur as an extension of the reaction in the pores.The base membrane will necessarily have a molecular weight cutoff whichallows passage of the reactants into the pores, so that and under theapplied conditions, e.g. of pressure, temperature, pH and ionicstrength, the concentration of the reactants within the pores willincrease, resulting in chemical reaction with covalent bond formation,which may include formation of coordinate covalent bonds and conjugatedbonds. This reaction occurs primarily and selectively within the uppersmallest pore volumes of the underlying membrane, and not significantlyin the solution or within the larger pores of the underlying structureof the support. A barrier is thus built up from the interior of thesepores and towards the upper exterior surface of the underlying membrane.The thickness and density of the materials in the pores is a function ofthe concentration and molecular weight of the reactants, the reactionconditions, the size of the pores in the upper layer of the asymmetricbase membranes being modified, and the duration of the application ofthe pressure.

Additional details concerning the nature of the underlying supportmembrane, reaction conditions, post-reaction processing, such asheating, and the like are described in WO 99/40996.

Applicants have discovered that halo-substituted di- and triazine-basedmembranes as described herein are surprisingly stable to acidicconditions compared to commonly used membrane materials and providemembranes for the separation of copper and other metals from liquidstreams that are more stable than those hitherto known. In some casesthis stability may be observed, for example, in that after acid exposureunder one of the conditions described above, the glucose rejection ofsuch membranes will not decrease significantly (e.g. 5% or less) but theflux may increase significantly (e.g. 20% or more.). It will beappreciated that in forming the membranes used in accordance withembodiments of the invention, it may be desirable to include functionalgroups to improve retention of multivalent cations and/or improve acidtransport. Such functional groups include but are not limited toderivatives of ammonium, phosphonium, and sulfonium.

DEFINITIONS

Unless stated otherwise, the following definitions apply.

The term “cationic functional groups” includes functional groups whichare cationic at virtually all pH values (e.g. quaternary amines) as wellas those that can become cationic under acidic conditions or can becomecationic through chemical conversion (i.e. potentially cationic groups,such as primary and secondary amines or amides).

The term “matrix” means a regular, irregular and/or random arrangementof polymer molecules such that on a macromolecular scale thearrangements of molecules may show repeating patterns, or may showseries of patterns that sometimes repeat and sometimes displayirregularities, or may show no pattern respectively. The molecules mayor may not be cross-linked. On a scale such as would be obtained fromscanning electron microscopy (SEM), X-Ray diffraction or FourierTransform Nuclear Magnetic Resonance (FTNMR), the molecular arrangementmay show a physical configuration in three dimensions like those ofnetworks, meshes, arrays, frameworks, scaffoldings, three dimensionalnets or three dimensional entanglements of molecules. The matrix isusually non-self supporting, and has an average thickness from about 5nm to about 600 nm, preferably about 5 to about 400 nm. In usualpractice, the matrix is grossly configured as an ultrathin film orsheet.

The term “membrane” means a semipermeable material which can be used toseparate components of a feed fluid into a permeate that passes throughthe material and a retentate that is rejected by the material.

The term “monomer” or “monomeric” means a compound that has no branchedor unbranched repeating units (e.g. ethylenediamine,1,3-metaphenylenediamine).

The term “oligomer” or “oligomeric” means a compound that has 2 to 10branched or unbranched repeating units (e.g. polyethyleneimine with 7repeating units, tris(2-aminoethyl)amine).

The term “polymer” or “polymeric”, when referring to a reactant, means acompound that has 11 or greater branched or unbranched repeating units(e.g. 20,000 MW polyethyleneimine).

The term “composite membrane” means a composite of a matrix layered orcoated on at least one side of a porous support material.

The term “support material” means any substrate onto which the matrixcan be applied. Included are semipermeable membranes especially of themicro- and ultrafiltration kind, fabric, filtration materials as well asothers.

The term “20% sulfuric acid” means a solution of deionized water and 20%sulfuric acid by weight. For illustration, “a feed solution consistingof 9.5% CuSO₄ and 20% sulfuric acid” can be prepared by combining 20grams of H₂SO₄, 9.5 grams of CuSO₄, and 70.5 grams of deionized water.

The term “average thickness” is the average matrix cross-sectionaldimension. It means the average distance in cross section from one sideof the matrix to the opposite side of the matrix. Since the matrix hassurfaces that are at least to some extent uniform, the average thicknessis the average distance obtained by measuring the cross-sectionaldistance between the matrix sides. Techniques such as ion beam analysis,X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy(SEM) can be used to measure this dimension. Because the cross-sectionaldimension usually is not precisely the same at all points of the matrix,an average is typically used as an appropriate measurement.

The term “acid stable” when referring to a matrix or polymer, or whenreferring to a linkage, means in the context of the present inventionthe polymer backbone is able to sustain useful membrane properties, orthat the linkage remains intact, after exposure to at least one of thetest exposure conditions set forth above.

The term “A value” in the context of the present application representsthe water permeability of a membrane and is represented by the ratio ofcubic centimeters of permeate water over the square centimeters ofmembrane area times the seconds at the pressure measured in atmospheres.An A value of 1 is essentially 10⁻⁵ cm³ of permeate over themultiplicand of 1 centimeter squared of membrane area times 1 second ofperformance at a net driving pressure of one atmosphere. Unless notedotherwise, in the context of the present application, A values givenherein have the following unit designation: 10⁻⁵ cm³/(cm²×sec×atm) or10⁻⁵ cm/(sec×atm) at 25° C.A=permeate volume/(membrane area*time*net driving pressure).

The term “flux” means the rate of flow of permeate through a unit areaof membrane. It should be noted that under most circumstances the fluxis directly related to the applied trans-membrane pressure, i.e., amembrane can provide a specific flux of permeate at a given pressure.This flux is often given in units of gfd.

The term “transmission value” means the solute concentration in thepermeate divided by the average of the solute concentration in the feedand in the concentrate, expressed as a percentage [i.e. transmissionvalue=permeate/((feed+concentrate)/2), expressed as a percentage]. Theconcentrate is the fluid that flows completely past, but not through,the membrane.

The term “retention value” means 100% minus the transmission value.

The term “recovery value” means the ratio of permeate fluid flow to feedfluid flow, expressed as a percentage.

The flux and retention values are measured when the membrane is operatedin crossflow mode involving a 34-mil mesh spacer commonly used in theart with less than 5% recovery across the membrane sample or whenoperated with at least a fluid Reynolds number of 1000.

The term “gfd” means gallons per foot² per day, viz gallons/(foot²×day).This is the flux rate at which permeate flows through the membranes.

The term “cation” means an ionized atom or molecular fragment that has apositive charge of at least one. The term “multivalent cation” means anionized atom or molecular fragment that has a positive charge of atleast two; these are typically metal atoms. Under these definitions,hydrogen (H⁺) and hydronium (H₃O⁺) ions are considered cations.

The term “net driving pressure” is equal to the average trans-membranepressure minus the osmotic pressure difference between the feed andpermeate.

The term “removing” means providing a retention value at the specifiedfeed composition and operational conditions. Thus “removing at least 50%of the copper ions” means “providing at least 50% retention value of thecopper ions”.

The term “continuous spaces” means pores, void spaces, or free volumeareas where the solutes can pass. These spaces can allow feed solutionto pass the membrane without significant retention of the desiredsolutes.

The term “polysulfonamide” means a polymer comprising sulfonamidelinkages in the polymer backbone. The term also includes polymerscomprising sulfonamide linkages and other acid stable linkages in thepolymer backbone. For example, a polysulfonamide can be prepared throughthe interfacial reaction of an amine monomer comprising two or moreprimary or secondary amine groups and a sulfonyl monomer comprising twoor more sulfonyl halides.

The term “aliphatic” or “aliphatic group” is known in the art andincludes branched or unbranched carbon chains which are fully saturatedor which comprise one or more (e.g. 1, 2, 3, or 4) double or triplebonds in the chain. Typically, the chains contain from 1 to about 30carbon atoms. In some embodiments, the chains contain from 1 to about 20carbon atoms. In some embodiments the chains contain from 1 to about 10carbon atoms. Representative examples include methyl, ethyl, propyl,isopropyl, pentyl, hexyl, propenyl, butenyl, pentenyl, propynyl,butynyl, pentynyl, hexadienyl, and the like.

“Alkyl” is a subset of aliphatic and is intended to include unsaturatedlinear, branched, or cyclic hydrocarbon structures and combinationsthereof. Lower alkyl refers to alkyl groups of from 1 to 6 carbon atoms.Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl,butyl, s- and t-butyl and the like. Cycloalkyl is a subset of alkyl andincludes cyclic hydrocarbon groups of from 3 to 8 carbon atoms. Examplesof cycloalkyl groups include c-propyl, c-butyl, c-pentyl, norbornyl,adamantyl and the like.

The term “aryl” denotes a phenyl radical or an ortho-fused bicycliccarbocyclic radical having about nine to ten ring atoms in which atleast one ring is aromatic. Representative examples include phenyl,indenyl, naphthyl, and the like.

The term “heteroaryl” denotes a group attached via a ring carbon of amonocyclic aromatic ring containing five or six ring atoms consisting ofcarbon and one to four heteroatoms each selected from the groupconsisting of non-peroxide oxygen, sulfur, and N(X) wherein X is absentor is H, O, (C₁₋₄)alkyl, phenyl or benzyl, as well as a radical of anortho-fused bicyclic heterocycle of about eight to ten ring atomsderived therefrom, particularly a benz-derivative or one derived byfusing a propylene, trimethylene, or tetramethylene diradical thereto.Representative examples include furyl, imidazolyl, triazolyl, triazinyl,oxazoyl, isoxazoyl, thiazolyl, isothiazoyl, pyrazolyl, pyrrolyl,pyrazinyl, tetrazolyl, pyridyl, (or its N-oxide), thienyl, pyrimidinyl(or its N-oxide), indolyl, isoquinolyl (or its N-oxide) quinolyl (or itsN-oxide), and the like.

The term “heteroaliphatic” or “heteroaliphatic group” is known in theart and includes branched or unbranched carbon chains wherein the chainis interrupted with one or more (e.g. 1, 2, 3, or 4) non-peroxy oxygen,sulfur or nitrogen atoms. Typically, the chains contain from 1 to about30 carbon atoms and from about 1 to about 10 heteroatoms. In someembodiments, the chains contain from 1 to about 20 carbon atoms and fromabout 1 to about 10 heteroatoms; in some embodiments, the chains containfrom 1 to about 10 carbon atoms and from about 1 to about 5 heteroatoms.Representative examples include 2-methoxyethyl, 3-methoxypropyl, and thelike.

The term “membrane is cationic” means that the membrane carries a netpositive charge. This can be measured, for example, by streamingpotential.

Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of astraight, branched, cyclic configuration and combinations thereofattached to the parent structure through an oxygen. Examples includemethoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, cyclohexyloxy andthe like. Lower-alkoxy refers to groups containing one to four carbons.

Acyl refers to groups of from 1 to 8 carbon atoms of a straight,branched, cyclic configuration, saturated, unsaturated and aromatic andcombinations thereof, attached to the parent structure through acarbonyl functionality. One or more carbons in the acyl residue may bereplaced by nitrogen, oxygen or sulfur as long as the point ofattachment to the parent remains at the carbonyl. Examples includeformyl, acetyl, propionyl, isobutyryl, t-butoxycarbonyl, benzoyl,benzyloxycarbonyl and the like. Lower-acyl refers to groups containingone to four carbons. Acylalkyl refers to a residue in which an acylgroup is attached to an alkylgroup which is attached to the parent. Anexample would be CH₃C(═O)CH₂—. Such residues could also be characterizedas “oxoalkyl” residues.

Arylalkyl means an aryl attached to the parent structure via an alkylresidue. Examples are benzyl, phenethyl and the like.

Substituted alkyl, aryl, cycloalkyl, heterocyclyl etc. refer to alkyl,aryl, cycloalkyl, or heterocyclyl wherein up to three H atoms in eachresidue are replaced with alkyl, halogen, loweralkyl, haloalkyl,hydroxy, loweralkoxy, carboxy, carboalkoxy (also referred to asalkoxycarbonyl), carboxamido (also referred to as alkylaminocarbonyl),cyano, carbonyl, nitro, amino, alkylamino, dialkylamino, mercapto,alkylthio, sulfoxide, sulfone, acylamino, amidino, phenyl, benzyl,heteroaryl, phenoxy, benzyloxy, or heteroaryloxy.

“Halogen” means fluorine, chlorine, bromine or iodine; “halo” meansfluoro, chloro, bromo or iodo.

The term “monolithic NF membrane” refers to an NF membrane in which theNF layer is covalently bound to the underlying UF support, which in turnis optionally covalently bound to its support (e.g. a non-woven or wovensupport).

The following is a general discussion of the state of the art precedingthe present invention:

In addition to the potential problems that can be caused by mechanicaldeformation as a result of action of hydrostatic pressures, the supportsthat are used for manufacturing MF, UF, PV and RO membranes are oftenmade from polymers that swell or dissolve in organic solvents, acids andcaustics, with the result that their mechanical properties are weakenedin such streams. Examples of solvents that are used in industry butwhich may weaken or destroy polymeric membranes are: dimethylformamide(DMF), N-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), hexamethylphosphoramide, sulfolane (tetramethylene sulfone),N,N-dimethylacetamide, acetone, hexane and other solvents. Swollenmembranes are mechanically weaker under conditions of appliedhydrostatic pressure and may undergo compaction deformation, loss offlux and resultant loss of performance.

Solvent stable UF/MF membranes are also described in the literature. Animportant group of membranes include those based on ceramic or otherinorganic materials. Some examples of specialized membranes made fromcross-linked polymers are also known in the art. The ceramic basedmembranes, however, are expensive, and available in only a very limitednumber of configurations with limited characteristics. Besides ceramics,membranes fabricated from cross-linked polymers such as epoxy polyimidetype polymers and encapsulated polymers are also available. Encapsulatedpolymeric membranes are described in U.S. Pat. Nos. 4,778,596 and6,086,764. These membranes are coated on the external surfaces and oninternal porous surfaces with a cross-linked polymeric layer. Thesupporting UF membrane backbone is not, itself, cross-linked, but ishowever, encapsulated by means of an outer skin. Consequently, suchmembranes do not generally possess stability in organic solvents andupon immersion in aggressive solvents tend to swell and disintegrate.

Stability is not the only criterion for useful and effective membraneseparation. Selectivity and optimized fluxes are generally essential forachieving the separation goal. In some applications very high retentionof all small soluble molecules is required. In other applicationsseparation between low molecular solutes from larger solutes is needed;thus selectivity is one of the parameters that must be achievedsimultaneously with the chemical, compaction and temperaturestabilities. At present, no single membrane type is available with allsuch properties that can provide an appropriate solution to all neededseparations, and specific combination of properties must be tuned toachieve acceptable stability and separation selectivity. No membranessuit all applications. Some membranes that are needed in the separationfield of ultrafiltration, nanofiltration, reverse osmosis,pervaporation, vapor permeation and catalysis are not available. Typicalexamples demonstrating limitations of the present membrane classes aregiven below.

Ceramic membrane supports have very good thermal stability exceeding250° C. They are also known to have good solvent stability and stabilityagainst attack in oxidizing media. However, their pressure stability,particularly of their tubular configurations, is limited in many casesto 20-30 bars only, while standard polymeric membranes for reverseosmosis can withstand pressures of up to 70 and even 80 bars in spiralwound configuration and in plate and frame configuration may exceed 120bars. The limited pressure stability of the currently available ceramicsupports in tubular or capillary configurations is a serious limitation,that limits the use of NF or RO membranes made on such ceramic supportsto streams with low concentrations of soluble matter that exert lowosmotic pressures where low hydrostatic pressures provide a satisfactorysolution.

In many cases the stability of ceramic membranes in harsh acidic oralkaline environments is inferior to the stability of some polymericsupports such as polyether ether ketone (PEEK), polyphenylene sulfone(PPSu) and even of polysulfone (PS) and polyethersulfone (PES). Ceramicnanofiltration membranes with tight molecular weight cutoff (MWCO˜200Daltons) are known and reported in the literature, but the selectivitybetween molecules of varying molecular weights is still limited and isinferior to the selectivity that can be achieved with a variety ofpolymeric thin film composite layers.

A class of hybrid ceramic polymeric membranes has been developed,allowing a variety of polymeric top layers to be coated onto ceramic UFsupports. Such polymer layers may be endowed with a variety of importantproperties, such as stability, selectivity and permeability in variousorganic solvents (WO 99/40996). It will be appreciated thatceramic-polymeric hybrids extend the range of achievable selectivitiesand the range of solvent and chemical stabilities of the ceramicmembranes but does not provide an adequate solution to their limitedstability in strong acids and bases and limited pressure stability.Another common problem of the ceramic membranes is their brittleness andvery high cost. These factors limit their use to only very specialcases.

A wide range of polymeric membranes can be used for making UF, NF, RO,PV and MF membranes and membranes for separations of catalysts. Some ofthese membranes such as PES, PS, PPSu, PPS (Polyphenylenesulfide), PPO(Polyphenyleneoxide) have excellent stability under high appliedpressure combined with good chemical resistance against attack inoxidizing media, but they lack stability in organic solvents. Asmentioned above, a combination of solvent stability with a chemicalstability in extreme pH conditions and in oxidizing environment isneeded for many industrial and wastewater applications, however thecombination of such properties is lacking in almost all currentlyavailable membranes.

Solvent resistant polymeric membranes for UF, NF & PV applications areknown. Typical polymers for making solvent resistant membranes are madefrom cellulose, polyacrylonitrile or poly-imides. These membranes do notpossess the required stabilities in strong acidic, alkaline andoxidizing media.

Cross-linked polyacrylonitriles disclosed in U.S. Pat. No. 5,032,282 arelimited in their acid and base stability (pH range 2-12), their thermalstability and their resistance to oxidants.

Cross-linked PANGMA disclosed in U.S. Pat. No. 6,159,370 has shown verygood solvent stability and is reported to have some stability in acidicmedia but has limited stability in concentrated caustic conditions andin concentrated acids. This material also has limited resistance tooxidizing media.

Solvent resistant polyimides have been developed, as described in U.S.Pat. No. 5,067,970, but lack stability in extreme pH conditions. Forexample, some typical polyimides degrade in 10% NaOH in a period of fewdays.

Many polymers are useful for making asymmetric types of membranes. Onedrawback of currently available membranes from these polymers is theirsensitivity to organic solvents. PAN, PVDF, PS, PES, PPSu and membranesthereof, swell and dissolve in many organic solvents such as acetone,toluene, n-butylamine, methyl chloride, methylethylketone, and the like.PAN membranes are also of limited use in presence of organic solventssince they tend to swell and dissolve in solvents such as DMFA, DMSO andNMP.

The patent literature includes many examples of modification proceduresto overcome these disadvantages, including U.S. Pat. No. 6,159,370, U.S.Pat. No. 4,477,634, European Patent No. EP 0574957 and U.S. Pat. No.5,032,282. However, such methods suffer from one or more disadvantagesor limitations, such as a need for toxic and expensive reagents, and/ororganic solvents, incomplete cross-linking and/or poor control over theextent of modification.

Other types of damage that can occur to multilayer membranes when usedin harsh conditions is delamination, i.e. the separation between thedifferent layers of the membrane due to their different degree ofswelling and thus different degree of dimensional change. This causesadjacent layers to separate and imparts substantial damage to both theperformance and working life of the membrane.

Solvent resistant membranes based on PAN and PVDF are known. They havebeen described in European Patent No. EP 0574957 and in U.S. Pat. No.5,032,282. Stability of solvent resistant membranes can be achieved bychemical modification of the entire polymeric matrix ofpolyacrylonitrile or polyvinylidene fluoride and their subsequentsurface cross-linking as is shown in the following description.

European Patent No. EP 0574957 states that PAN and PVDF membranes werecross-linked by immersion for 5 minutes in 1% wt/vol. sodium ethoxide,drained and then heated to 115° C. for 30 minutes. It is well known inthe state of the art to perform such a reaction throughout the wholebulk of a polymer or membrane. There are many known polymeric productsbased on this approach, including ion exchange resins based oncross-linked polystyrene, electrodialysis membranes, epoxy resins andother similar materials.

Usually the formation of such cross-linked products is done by mixingchemically reactive monomers with cross-linking agents, initiators andother additives. The cross-linking reaction occurs in the entire bulk ofa polymer and involves high bulk density of covalent cross-linkingbonds. Such methods of making cross-linked polymeric products aresuitable for imparting a desired combination of chemical and solventstability properties to a final polymeric product.

However, such manufacturing methods for making cross-linked, chemicallystable polymeric products are limited to a narrow range of membranetypes, particularly for making flat homogenous membranes.Electrodialysis membranes of this type have a thickness of 0.1-0.2millimeters and are essentially homogenous throughout theircross-section. These methods can also be used for making thin coatingson porous substrates such as top layers of NF, RO, PV and similarmembranes types.

A major class of pressure driven membranes, such as MF, UF, NF, RO, PVand gas permeating membranes, have asymmetric structures and suchmembranes are made by a well known phase inversion process, in which asolution of a polymer in an organic solvent or solvent mixture is castfirst as a flat layer and then immersed in a water bath, therebyimparting an asymmetric structure to the membrane.

There is very large class of polymers that can be cast into anasymmetric form in such a manner, mainly as MF or UF membranes, butsometimes as NF and RO membranes. The most well known are those madefrom PAN, PVDF, polyimide, polyamide, PS, PES, PPSu, cellulose,cellulose acetate and others. As mentioned, most of such membranes lackone or more commonly desired resistances, and desired combinations ofstability properties such as chemical, oxidation, thermal and solventstabilities have not hitherto been available, and certainly not atcommercially viable prices.

Cross-linking methods based on development of special copolymers areusually complicated, involving difficult chemical reactions. In manycases special copolymers must be manufactured in order to insert into achain of the main polymer, an appropriate chemically reactive group thatis capable of performing a cross-linking chemical reaction throughoutthe polymer structure.

It will be appreciated that in order to perform a cross-linkingreaction, a low MW cross-linker must penetrate into the bulk of apolymeric backbone and react with the reactive functional groups. Anexample of such a cross-linking method is a solvent stable membranepresented in U.S. Pat. No. 6,159,370 (Hicke et al.), wherein a method ofmanufacturing a polyacrylonitrile copolymer by reacting acrylonitrilewith glycidylmethacrylate groups is described. A completely new polymermust be manufactured which is both complicated and costly. Such apolymer is first cast into an asymmetric membrane and subsequentlycross-linked using ammonia as the cross-linker.

The complexity and costs of implementation of such a method areself-evident. Such an approach for making solvent and acid resistantmembranes has several drawbacks:

(a) A new polymer must be synthesized from monomers, which is not acommercial process. This requires specialized synthetic facilities andresults in a high cost raw polymer for making such membranes. It will beappreciated that the production of commercial quantities requiressignificant investment and is more expensive than purchasingcommercially available polymers that are conventionally used for makingmembranes.

(b) A new casting formulation must be developed every time a new polymeris developed and synthesized.

(c) The cross-linking reaction is complicated and requires use ofaggressive and poisonous reagents (gaseous ammonia) and reactors thathave negative environmental effects.

(d) The reaction requires expensive equipment and can be carried outonly in small production batches, again adding to the cost of themembranes produced by such an approach.

Direct modification of PAN by monomeric amines involves manydifficulties. As is known, hydroxylamine can react in mild conditionswith aliphatic, aromatic and polymeric nitriles by forming amidoximegroups at high conversion (“The Chemistry of the Cyano Group”, F. C.Schaefer ed. Z. Rappoport, Interscience, New York, chapter 6, p.239-305, (1970); “The Chemistry of Amidoximes and Related Compounds”, F.Eloy and R. Lenaers, Chem. Rev., 62, p. 155, (1962)).

Polyacrylonitrile has been cross-linked throughout the whole membranematrix by thermal methods (U.S. Pat. No. 5,039,421). In this case theincrease of temperature, in a type of a pre-pyrolysis step, leads to aconversion of acrylonitrile groups into cyclical structures. While ahighly cross-linked membrane was formed with very good solventstability, the PAN backbone is vulnerable to decomposition at extremeacidic or alkaline conditions and to oxidants.

U.S. Pat. No. 4,477,634 describes a process for modifying PAN through areaction of (a) hydroxylamine as a first step for convertingacrylonitrile groups of PAN into amidoxime groups and (b) apolyfunctional ionic cyclic carbonic acid amide-halide (cyanuric acid)capable of reaction with the amidoxime groups. Only a partlycross-linked PAN membrane is formed, due to the low conversion of thenitrile groups of PAN to amidoxime. Only about a 20% conversion of thenitrile groups is obtained, even though the reaction is typicallyeffected at 60° C.

Such a low conversion value demonstrates the difficulties of polymermodification under heterogeneous conditions. By using only the firststep above, the nitrile groups are converted into amidoxime withoutimparting to the membrane any degree of cross-linking. The use of asecond step is essential for cross-linking, since only then a reactionof the amidoxime groups with carbonic acid imide-halide forms covalentbonds, thereby imparting stability in solvents and acids to themembrane.

Such modification of membranes is carried out in two steps and involvesa very difficult technological process using labile, toxic compounds.This is particularly true in respect of the second step of the process,which employs a 2% cyanuric chloride suspension at 0-5° C. It willfurther be appreciated that the high consumption of cyanuric chlorideand large quantities of water create significant ecological problems,and dealing with this in an appropriate manner adds to the costs ofproduction.

There are other possible methods for cross-linking polyacrylonitrilepolymers. For example, it is known from the literature that the nitrilegroups present can react with amine groups to produce an amidine (“TheChemistry of the Cyano Group” F. C. Schaefer ed. Z. Rappoport,Interscience, New York, chapter 6, p. 239-305 (1970)). However, thesereactions require extreme reaction conditions such as high temperature,pressure, anhydrous solvents and catalysts.

Solvent resistant polyimides have been made by first casting polyamicacid and then heating. Solvent resistant polyimide membranes have beenmade by casting unsaturated polyimides, as described for example inEuropean Patent No. EP 0 422 506 A1, Burgoyne, et al, which can becross-linked through the double bonds by free radicals or ionizingradiation. Solvent stable membranes based on an aromatic polymer havinga thio ether can be made by oxidizing the membrane, thereby making theminsolubilized, as described in Nakashima et al, U.S. Pat. No. 5,272,657.

In some cases the cross-linking is achieved as a result of a completechange in the chemical nature of the starting polymer. For example, acellulose derivative can become solvent resistant by hydrolyzing most ofits acetate groups, thereby converting it to essentially insolubleregenerated cellulose. This material can then be converted into acompletely cross-linked structure by reacting with either abi-functional or a multi-functional reactant.

In U.S. Pat. No. 5,282,971 (P. J. Degen, J. Lee, Pall Corp., Feb. 1,1997), polyvinylidene fluoride MF membranes are positively charged onall their external and internal surfaces by exposing the membrane toionizing radiation (gamma and electron radiation), which producesradicals on the membrane, and then contacting it with an aqueoussolution containing vinyl monomers, at least some of which arecationically charged (most preferably using diallyldimethyl ammoniumchloride), and non-ionic but polar monomers (e.g., HEMA). Afterirradiation and polymerization, the membrane is washed to remove polymerthat is not bound to the membrane.

In U.S. Pat. No. 4,778,596 to Linder et al. (Oct. 18, 1988) asemipermeable membrane is formed by first coating by immersion all theexternal and internal surfaces with a coating polymer and thencross-linking this external coating polymer by immersion in anothersolution containing a cross-linker. The cross-linker diffuses into thecoating and cross-links both external and internal coatings, however,membranes formed in this manner do not possess the stability in organicsolvents necessary for many applications.

In U.S. Pat. No. 4,704,324 to Davis, composite membranes are formed byplacing a thin layer of solution containing reactive cationic compoundwith a compound containing a nucleophilic moiety. The reaction productcontains covalent bonds formed via charge elimination reactions andgives a cross-linked selective layer on the upper surface of a poroussupport. However, this method does not form a solvent stable membrane.

Accomplishing reactions of the amine groups with nitrile or halogencompounds of PVDF membranes is very difficult. An example of this can befound in results of research on the PVDF reactions with amines invacuum, at temperature of 80° C. appearing in H. Schonhorn and J. P.Luongo, J. Adhesion Sci. Technol., Vol. 3, N4, pp. 227-290, (1989).There it was shown that amine and amide curing agents for epoxy resinsserve a dual function. They react both with the fluoropolymer to modifythe surface region and to cross-link the epoxy resin. This publicationdoes not disclose any solvent and acid resistant surface modified PVDFpolymer matrix.

It is also known that the cross-linking mechanism of diamines withVDF-based fluoro-polymers may proceed in three main steps: eliminationof HF (dehydrofluorination) from VDF segments to generate internaldouble bonds; Michael addition of the diamine onto the resulting doublebonds to form cross-links, and elimination of HF from the cross-linksduring post-cure, to form further double bonds.

The mechanism of cross-linking with diamine (for example forhexamethylenediamine) with a poly(VDF-co-HFP) copolymer is described inan article by A. Taguet, B. Ameduri and B. Boutevin, J. Adv. Polym.Sci., 184, p. 127-211 (2005). This mechanism occurs in the course of thepress-cure treatment of polymer at 150-170° C., ˜30 min. In a firststep, the diamine dehydrofluorinates the VDF/HFP diad, creating a doublebond. Then, by Michael addition, the diamine adds onto two CF═CHunsaturated backbones, creating bridges between polymeric chains. TheCF═NH bonds are sensitive to the oxygen atmosphere and to heating, andsubmit to a further dehydrofluorination leading to a C═N bond that candegrade into a C═O bond.

Thus, reaction of the PVDF with amines in heterogeneous conditionscannot be controlled and cannot be stopped at a desirable stage. It canbe reasonably assumed that the modification process occurs on thesurface and not in the bulk of the polymeric film. By contrast, in thecase of modification of the polymeric films and membranes on a PAN orPVDF basis by low molecular weight amines that provide new propertiessuch as solvent and acid resistance, it can be assumed that bulkmodification does occur.

Semi-permeable membranes have a long history of use in separatingcomponents of a fluid mixture such as a solution or a suspension. In thecontext of such separations, such membranes preferentially retaincertain components while preferentially allowing other components topass through the membrane. The components of the feed fluid that passthrough the membrane are generally referred to as the “permeate” andthose that do not pass through the membrane (i.e., are rejected by themembrane or are held by the membrane) are generally referred to as the“retentate”. Depending on the specific application, the permeate, theretentate, or both streams may constitute or be enriched in the desiredcomponent(s), and may be used as obtained from the membrane, or may besubjected to further processing. In order to be economically viable, themembrane must provide sufficient flux (the rate of permeate flow perunit of membrane area) and separation (the degree to which the membraneis able to retain certain components while allowing others to passthrough).

The degree of separation and permeate flux obtained in a membraneseparation process are determined in large part by the generalmorphology of the membrane, together with its physiochemistry. Dependingon the membrane formation technique employed, a given polymer type canbe used to fabricate a wide variety of membranes including those withrelatively large pores, those with smaller pores, or even those withpores sufficiently small that solute transport through the membrane isgoverned by the interactions among specific chemical functional groupsin the membrane polymer and the feed components.

Semi-permeable membranes can be described by several differentclassifications. One method of classifying liquid permeating membranesis to refer to them as microfitration (MF), ultrafiltration (UF),nanofiltration (NF), or reverse osmosis (RO) membranes. These classesare not based on any single exact, formal definition, but arenevertheless terms commonly used and understood in the membraneindustry.

In general, the term “microfiltration membranes” refers to thosemembranes with pores having an average diameter of greater than about0.1 microns. The upper pore size limitation of mictrofiltrationmembranes is not strictly defined, but can be considered to be about 10microns. Materials with pore sizes larger than about 10 microns aregenerally not referred to as membranes. Microfiltration (MF) membranesare commonly used to retain small particulates and microbes. Typically,these membranes allow the permeation of smaller components, such assimple salts, dissolved organic materials having a molecular weight ofless than about 100,000 and colloidal particles that have physicaldimensions that are smaller than pores of MF membrane. MF membranesusually possess the highest water permeability of the four classes ofmembranes, due to their large pore diameters as well as their typicalhigh pore density. The pure water permeability (A value) of thesemembranes is commonly greater than about 5,000 liter/(m²×h×bar).

Ultrafiltration (UF) membranes typically are characterized by pore sizesof from about 0.1 micron to about 5 nanometers. UF membranes arecommonly classified by their ability to retain specific-sized componentsdissolved in a solution. This is referred to as the molecular weightcut-off (MWCO). UF membranes are commonly used to retain proteins,starches, and other relatively large dissolved materials while allowingthe permeation of simple salts and smaller dissolved organic compounds.The water permeability of UF membranes is commonly in the range of fromabout A=100 liter/(m²×h×bar) to about A=5000 liter/(m²×h×bar).

Nanofiltration (NF) membranes typically are defined as membranes whichpossess the ability to fractionate small compounds (i.e., those withmolecular weights less than 1000). The small compounds are often salts,and NF membranes are commonly used to permeate monovalent ions whileretaining divalent ions. NF membranes typically possess ionized orionizable groups on their surfaces, including within the pores. Althoughnot wishing to be bound by theory, it is believed that NF membranes caneffect the separation of ionic materials through a charge-basedinteraction mechanism. NF membranes also can be used to separateuncharged organic compounds, sometimes in solvents other than water orto separate organic molecules from salts. The water permeability of NFmembranes is commonly in the range of from about A=1 liter/(m²×h×bar) toabout A=10 liter/(m²×h×bar).

Reverse osmosis (RO) membranes can retain all components other than thepermeating solvent (usually water). Like NF membranes, RO membranes cancontain ionic functional groups. RO membranes are commonly used toremove salt from water and to concentrate small organic compounds. Thewater permeability of reverse osmosis membranes is commonly in the rangeof from about A=0.2 liter/(m²×h×bar) to about A=5 liter/(m²×h×bar).

Although the mechanisms that govern membrane performance are not exactlydefined, some basic theories have been postulated. A good review of somemembrane transport theories can be found in The Solution DiffusionModel: A Review, J. G. Wijmans, R. W. Baker, J. Membrane Science, 1995,vol. 107, pp. 1-21, the contents of which are incorporated herein byreference.

It is generally believed that microfiltration and ultrafiltrationoperate via a pore flow model where the pores of the membrane sieve thecomponents of the feed solution through primarily physical interaction.Chemical interactions between the chemical functional groups on the porewall and the chemical functional groups of the feed solutions arebelieved to generally play only a minor role in governing separation bymicrofiltration and ultrafiltration membranes.

With regard to NF and RO membranes, the general belief is that thesemembranes effect separation through both physical and chemicalinteractions. It is believed that since the pore sizes of thesemembranes are so small—thought by some to be simply the void spacebetween atoms or chains of atoms—large particles are retained by thesemembranes because they are physically too large to pass through themembranes. The transport of small components is thought to be governedin part by size-based sieving, as with MF and UF membranes, but also tobe influenced by interactions between the membrane material and thesolute. An NF membrane having an abundance of negatively chargedfunctional groups, for example, will tend to preferentially retainmultivalent anions over multivalent cations due to charge repulsion(while maintaining charge neutrality in both the permeate and theretentate). A membrane with a net positive charge will tend to retainmultivalent cations over multivalent anions.

Membranes have also been used in other applications such aspervaporation and gas separation. Typically, in these applications, themembranes permeate gaseous rather than liquid materials. Some membranesused in RO and NF have been found to function suitably in pervaporationand gas separation.

In addition to the functional classification of liquid-filteringmembranes as MF, UF, NF or RO, semi-permeable membranes also can beclassified by their structure. Examples are symmetric, asymmetric, andcomposite membranes. Symmetric membranes are characterized by having ahomogeneous pore structure throughout the membrane material. Examples ofsymmetric membranes are some MF membranes, many ceramic membranes, andtrack-etched microporous membranes.

Asymmetric membranes are characterized by a heterogeneous pore structurein at least part of the membrane material. Most commercially availableUF membranes posses an asymmetric structure.

Composite membranes are defined as having at least one thin film (alsosometimes called a matrix) layered on a porous support membrane. Thepores of the thin film layer are usually smaller than those of theporous support membrane, which is commonly a polymeric UF or MFmembrane. The thin film is usually a polymer layer of a thickness ofless than about 1 micron. Composite membranes of this type are usuallyasymmetric, but not all asymmetric membranes are composite membranes.While many types of separations involving a wide range of feed solutionshave been made possible through the use of semi-permeable membranes,some feed solutions contain substances that cause the degradation of themembrane or membrane performance and render the membranes impracticalfor separation of these feed solutions. A decline in performance can becaused by alterations in the morphology and/or the physio-chemicalintegrity of the membrane. For example, a feed solution can includesubstances that interact with membrane components to plasticize,dissolve or react with them chemically, thus degrading the membranestructure and/or function. Examples of substances that may degrademembrane components include acids, bases, oxidants, many organicsolvents and the like. Thus solvents can often plasticize or dissolvemembrane components.

The chemical mechanism of action of acids on various chemical functionalgroups is well known. Without wishing to be bound by theory, it isbelieved that the most useful definitions and descriptions of an acidare those referred to as a Lewis acid or a Brønstead acid. A Lewis acidis a compound that is capable of accepting electrons. The morecolloquial usage of the term “acid” is that of a Brønstead acid, i.e. acompound that can donate one or more protons. Brønsted acids all exhibitLewis acidity because the proton of a Brønsted acid is capable ofaccepting electrons. Examples of Brønsted acids include acids such as,for example, sulfuric acid, phosphoric acid, nitric acid, hydrochloricacid, and acetic acid. Similarly, examples of Lewis acids include borontrifluoride, aluminum trichloride, and iron trichloride.

Both Lewis and Brønsted acids are capable of promoting polymerdegradations. In aqueous media, this process is often referred to asacid hydrolysis. When acids attack the polymers of a semi-permeablemembrane, the degradation often is evidenced by an increase in permeateflow through the membrane, a decrease in solute rejection by themembrane, or a combination of changes in both of these performanceproperties. Significant changes in either of these properties can makethe use of a membrane for separation impractical. Commonly, this type ofperformance degradation is observed when commercial polyamidenanofiltration (NF) and reverse osmosis (RO) membranes are utilized toprocess strongly acidic feeds. Although initially their performance maybe sufficient to perform the desired separation, the performance rapidlydeteriorates, i.e. within a short period of time operating understrongly acidic conditions, the membranes lose the ability to retaindissolved metals, such as, cations and/or organic compounds.

The use of nanofiltration membranes for separation of copper and othermetals from metal-containing liquids is well known and documented in thetechnical and commercial literature. For example, copper is oftenleached from copper-containing ore using sulfuric acid. The copper maybe recovered by a combination of solvent extraction (SE), ion exchange(IE) and electrowinning (EW), but the use of NF membranes to filtercopper ions from copper-ion containing streams in such processes, eitherto improve the recovery of copper and/or to purify waste streams and/orto purify the acid for re-use, is known in the art. Thus, the use ofnanofiltration membrane for concentrating copper from an acidic processstream prior to its recovery by a subsequent SE, or ion exchange (IE)and/or EW process, or for improving the yield of the process byfiltering the acidic raffinate stream and recycling the filtered copperback into the process stream, is known in the art.

Typical processes in which NF/UF and MF membranes were used in copperand/or metal recovery are described in detail in the following patentpublications: U.S. Pat. No. 5,116,511, U.S. Pat. No. 5,310,486, WO94/27711, U.S. Pat. No. 5,476,591, WO 95/30471, U.S. Pat. No. 5,733,431,WO 99/023263, WO 00/50341, U.S. Pat. No. 6,156,186, U.S. Pat. No.6,165,344, U.S. Pat. No. 5,961,833 and U.S. Pat. No. 6,355,175(hereinafter collectively “the HW patents”). The disclosures of theseand all other patent publications mentioned herein, as well as thedisclosures of non-patent publications mentioned herein, areincorporated herein by reference.

Thus, for example, U.S. Pat. No. 5,116,511 describes an ion exchangeprocess for recovering copper and other metal ions from acidic wastewater; waste acid from this process may be filtered through “asemi-permeable membrane having micro-pore structure which prevents thepassage of metal ions therethrough while allowing the passage of primaryacid solution through the membrane.”

U.S. Pat. No. 5,310,486 and the corresponding WO 94/27711 disclose theuse of a nanofiltration membrane to filter metal-ion containingwastewater to remove the majority of ions thereform, then passing theacidic permeate through metal-absorbing beads to remove any remainingmetal ions from the permeate. The metal-containing retentate “is removedfrom the system for storage and/or disposal”. The metal is notrecovered, the emphasis being on purifying the acid sufficiently forre-use in IE/EW processes.

Similarly, U.S. Pat. No. 5,476,591 and the corresponding WO 95/30471disclose a process for the removal of copper and other metal ions fromwaste water in metal leaching processes. The waste water is passedthrough a nanofiltration membrane, which “produces a concentrated metalion-rich retentate which is prevented from passing through the membranesystem and a permeate which readily passes therethrough. Theconcentrated retentate is removed from the system for storage and/ordisposal while the permate (which has relatively low amounts of residualdissolved metals therein) is directed into a first treatment column forthe removal of any additional/residual dissolved metals (e.g. metalions) not removed by the nanofiltration system.” Alternatively, acidiclixiviant from copper leaching may be passed through a nanofiltrationmembrane, and the copper-ion rich retentate may then be treated torecover the copper, using known techniques such as solventextraction/electrowinning.

U.S. Pat. Nos. 5,733,431 and 6,165,344 disclose a method for removingsolid wastes from an organic extractant-based solvent extraction(SX)/electrowinning (EW) copper processing system. A lixivant isinitially applied to copper ore, followed by mixing of thecopper-containing lixivant product with an organic extractant. Theorganic extractant (which contains extracted copper ions) is thencontacted with an electrolyte solution. At least part of the remainingorganic fraction after electrolyte contact is passed through afiltration membrane (either an ultrafiltration or microfiltrationmembrane, not a NF membrane) to remove solid wastes. The filteredorganic fraction is then reused within the system, followed byelectrowinning of the copper-containing electrolyte to recover purifiedcopper. Alternatively, the organic extractant may be membrane-filteredafter initial contact with the copper-containing lixivant product toremove solid wastes from the organic extractant.

U.S. Pat. Nos. 5,961,833 and 6,355,175 disclose a method for separatinggold (or silver) ions from copper ions. Complexes of the metals withcyanide are formed in situ and then filtered at basic pH using ananofiltration membrane; the copper complexes are retained in theretentate and the gold complexes pass through in the permeate.

U.S. Pat. No. 6,156,186 and the corresponding WO 99/23263 disclosevarious processes for separating and in some cases recoveringmultivalent ions from process streams in leaching processes. In somecases, the desired metal, such as copper, is filtered from a wastestream by nanofiltration and then recovered using a combination ofeither solvent extraction or ion exchange, followed by electrowinning.In other cases, a metal other than copper is present in the retentateand the copper is present in the permeate; the copper may then berecovered by a further filtration step.

WO 00/50341 discloses a process for making sulfuric acid. The acid maybe further purified by a process that includes, inter alia, the removalof multivalent metal ions from the acid by nanofiltration. The metalsmay optionally be recovered by precipitation, electrolysis, ion exchangeresins, cementation or solvent extraction.

U.S. Pat. No. 5,547,579 (Brown; Eco-Tec Limited) discloses a process forpurifying acid by using a nanofiltration membrane in conjunction with anacid absorption unit.

U.S. Pat. No. 7,077,953 (Ranney; Harris Group, Inc.) discloses a processin which a nanofiltration unit is utilized to separate sugars from acidin sugar processing.

U.S. Patent Publication 2007/0125198 (Rossiter) uses a nanofiltrationmembrane clean up an acid process stream and to facilitate the recoveryof copper in a continuous process that also uses ion exchange and SX/EW.

U.S. Pat. Nos. 6,835,295 and 6,733,653 (Jangbarwala; Hydromatix, Inc.)disclose a process which uses a NF membrane in an electrowinningapparatus—metal-ion containing solution is drawn from near the cathode,filtered, and the metal-ion enriched retentate is recirculated toincrease Cu ion concentration in the apparatus. The permeate isdiscarded or processed separately. The use of an ion exchange column torecover Cu from semiconductor wafer fabrication is also discussed.

WO 03/035934 (Brown; Eco-Tec Limited) discloses a method for recoveringacidic pickling solutions (from stainless steel finishing processes)containing peroxide and dissolved metal. Nanofiltration is used toseparate metals from the solution; in order to reduce membranesusceptibility to hydrogen peroxide, the filtration is conducted at lowtemperature.

U.S. Pat. Nos. 5,587,083 and 5,858,240 (Twardowski; ChemeticsInternational Company, Ltd.) discloses the nanofiltration of aqueoussalt solutions to separate monovalent anions (such as chloride) frommultivalent anions (such as chromate).

U.S. Pat. Nos. 5,458,781 and 5,158,683 (Lin, Ethyl Corporation)discloses the nanofiltration of aqueous bromide solutions to separatemonovalent bromide from multivalent anions.

U.S. Pat. No. 6,843,917 (Gut et al.; Universite Claude Bernard Lyon)discloses a method for separating lanthanides and actinides by formingcomplexes of these atoms with chelators and then separating thecomplexes by nanofiltration.

U.S. Patent Publication 2003/0089619 (Jayasekera et al.) discloses aprocess for the electrowinning of copper, which involves the formationof copper-cyanide complexes followed by the separation of the complexesinto copper and cyanide ions. The copper ions are recovered byelectrowinning, and nanofiltration is used to recover the cyanide ions,which unlike multivalent ions present in the system pass through in thepermeate.

U.S. Pat. No. 6,827,856 (Desantis et al.; Bracco Imagin S.p.A.)discloses the use of a polyamide NF membrane to filter copper ions andpass iodide in the permeate as part of the X-ray contrast agentproduction process

U.S. Patent Publication 2008/0069748 (Lien et al.; HW AdvancedTechnologies, Inc.) discloses a process which uses a NF membrane toseparate Fe³⁺/Fe₂O₃ (retentate) from Fe²⁺/FeO (permeate, which is ofinterest to the inventors and recycled back into the system). Optionallythe Fe³⁺ ions may be complexed with a binder to increase theirlikelihood of being retained. Other “valuable metals” are from theretentate by EW and SX/IE.

U.S. Pat. No. 5,945,000 (Skidmore et al.; J.R. Simplot Company)discloses a process for purifying phosphoric acid by filtering crudephosphoric acid through a polyamide NF membrane to obtain purerphosphoric acid; by filtering at lower temperatures than was previouslydone, the life of the polyamide NFMs is reported to be lengthened.

U.S. Patent Publication 2008/0000809 (Wang et al.; GE Global Research)describes the use of an organic solvent-stable NF or RO membrane tofilter a hydrocarbon feedstock to remove vanadium therefrom. Althoughthe membranes are said to be “stable” to the solvent, no actual examplesof such membranes or their synthesis are provided.

The NF membranes employed in the HW patents are polyamide NF membranes;many NF membranes known in the art are based on polyamides or polyamines(see, e.g. U.S. Pat. No. 5,152,901 (Hodgdon; Ionics, Incorporated)).There is no discussion in the HW patents of the stability, or lackthereof, of the NF membranes employed. However, it was subsequentlyfound that the polyamide NF membranes degraded in the acidic environmentand had to be replaced approximately every 3 to 6 months.

It is therefore preferable to use for the copper recovery fromlixiviation solution NF membranes with high stability in acidicenvironments. Standard NF membranes are made from polyamides that lackthe necessary stability and must be replaced every 3-6 months.

U.S. Pat. No. 7,138,058 (Kurth; GE Osmonics, Inc.) discloses an NFmembrane that is reported to have a particular stability to sulfuricacid. The membrane is produced using an interfacial reaction of an amineand sulfonyl chloride to produce a polysulfonamide-based membrane. Whileproviding an improvement over earlier polyamide type membranes, thesulfonamide membrane is difficult to produce, let alone to produce withthe consistency required for commercial applications.

Platt et al., J. Membrane Science 239 (2004) 91-103 reported that two NFmembranes made from melamine polyamine are more stable than twocommercially available NF membranes in sulfuric acid.

U.S. Pat. Nos. 6,132,804 and 6,536,605 (Rice et al., Koch MembraneSystems, Inc.) describes an attempt to provide chemically stablemembranes using polyamine and cyanuric chloride. The performance of theKoch membranes is highly disappointing and these membranes do not havethe required chemical stability for use in aggressive process streams.

Another issue of importance in the copper recovery and metal recoverymining industry is the issue of copper recovery and copper losses.Copper recovery methods disclosed in the technical, patent andcommercial literature, including many of the patent publicationdiscussed above, achieve recovery rates of around 50%. U.S. Pat. No.5,476,591 discloses a process in which a copper ore is treated withacidic lixiviant solution, which is then passed through a nanofiltrationmembrane to produce copper concentrate and acid permeate. In order toavoid precipitation of mineral salts (Ca, Mn, as sulfates), this processincludes the addition of anti-scalants. However, the maximum copperrecovery achievable by operating in this manner is only about 50%. As aresult the copper concentration increases from ˜1100 ppm to about 2200ppm only. The copper concentrate is usually extracted from the pregnantleach solution (PLS) by means of solvent extraction, and since about300-500 ppm copper are usually left in the raffinate, this leads to asubstantial loss of copper, in the range of 10-30%.

In addition, in cases in which copper is extracted by SE processes, itmay be desired to recover copper from the raffinate stream. As theconcentrate of extracted copper increases, the concentration of acid inthe raffinate stream likewise increases. For example, if theconcentration of copper in the pregnant leach solution (PLS) to beextracted is 2000-3000 ppm (corresponding to a pH of around 3-3.5), thepH of the resulting raffinate stream will be around 1.5-2. If theconcentration of copper in the PLS is 10,000-20,000 ppm, the pH of theraffinate may be in the range 0.5-1. NF membranes which are currentlyused for copper recovery from raffinate streams, even those that areconsidered to be “acid stable”, are not stable at such low pH's and haveshort operating lifetimes under these conditions, making their use forcopper recovery from such raffinate streams economically prohibitive.

Polymeric membranes with stability toward acids are known. Examples ofpolymers that are relatively stable toward acids and can be used toprepare membranes include polyolefins such as, for example, polyethyleneand polypropylene, polyvinylidene fluoride, polysulfones,polyethersulfone, and polyether ketones. However, when these polymersare used in a dense film capable of retaining a high degree of dissolvedmetal cations and/or organic compounds, they are unable to permeateacids effectively. Conversely, when these polymers are used to form moreporous, less dense morphologies, the resulting polymeric membranes cantransmit a high degree of the dissolved acids, but then the membranesare unable to effectively separate dissolved metal cations and/ororganic compounds. In discussing polymers in the context of thisapplication, it will be appreciated that polymers typically areidentified by the chemical functional groups that are formed, or areused to form, the resulting polymer backbone. Polyamides, for example,are termed as such because those polymers typically are formed throughamide bond formation (even though such polyamide polymers may have onlya small amount of backbone that comprises amide linkages). As isunderstood by persons skilled in the art, it is the sum total of all theatoms and bonds in a polymer that are responsible for the performance ofa given polymer. Similarly, sulfonamide polymers include sulfonylcompound residues having at least two sulfonyl moieties and aminecompound residues having at least two amine moieties wherein thesulfonyl and amine moieties form at least some sulfonamide groups. Thesulfonamide polymer contains at least some sulfonamide linkages in thebackbone of the polymer. Other functional and/or nonfunctional linkagessuch as amide, ester, ether, amine, urethane, urea, sulfone, carbonate,and carbon-carbon sigma bonds derived from olefins may also optionallybe present in the backbone.

The preparation and the utility of the membranes will now bedemonstrated by means of the following non-limiting examples:

EXAMPLES Example 1

PAN/UF support membranes (PAN-400 and PAN-50 purchased from CUT MembraneTechnology GmbH & Co., Dusseldorf, Germany; and PAN-GMT-L1 purchasedfrom GMT Membrantechnik GmbH, Rheinfelden, Germany) were modified byimmersion in a 4% polyethylenimine (PEI) solution (2% PEI, MW=750,000;2% PEI, MW=800) followed by heat-treatment in a reactor at 90° C. for 17hrs. Then, the membranes were dried by air flow at 90° C. for 1 hr andfinally washed.

The following test method was carried out:

Test Method

Membrane performance (permeability) was measured using a magneticallystirred test cell at a pressure of 1 bar supplied from a compressednitrogen gas cylinder. The cell was a stainless steel cylinder having atits bottom a sintered stainless metal plate supporting the membrane.Reverse osmosis water (ROW) was introduced to the test cell and permeatewas allowed to accumulate and measured versus time.

The result of modification of different commercial PAN/UF membranes issummarized in Table 1.

Table 1 demonstrates that the modification by PEI leads to a new UFmembrane with a different membrane performance.

TABLE 1 Type of commercial Before modification After modification PAN/UFsupport Permeability Permeability membrane (L/m2*h*bar)/ROW(L/m2*h*bar)/ROW PAN-400 560 68 PAN-50 154 17 PAN-GMT-L1 109 11

Example 2

Membranes prepared in accordance with the procedure of Example 1 wereplaced in N-methylpyrrolidone for a period of 1 month. After thisexposure, the membranes were removed and their performance was measuredusing the test method described in Example 1. The results for themembranes' performance are summarized in Table 2.

Table 2 demonstrates the solvent stability of the PEI modified UFmembranes compared to the initial commercial membranes. After exposureto N-methylpyrrolidone, the non-modified commercial UF membranesdissolved, but the PEI modified UF membranes remained intact andmaintained their performance.

TABLE 2 Permeability (L/m2*h*bar) ROW Commercial UF membrane PEImodified membrane PAN-GMT- PAN-GMT- Membrane L1 PAN-400 L1 PAN-400Before the 109 560 11 68 immersion in N-methyl- pyrrolidone After theDissolved Dissolved 15 69 immersion in N-methyl- pyrrolidone for 1 month

Example 3

A PAN-GMT-L1 UF support membrane was modified in accordance with theprocedure of Example 1. The procedure was modified by using 4% PEI oflow molecular weight (MW=800). The membrane was tested in accordancewith the test method described in Example 1. The results are shown inTable 3.

Example 4

A PAN-GMT-L1 UF support membrane was modified in accordance with theprocedure of Example 1. The procedure was modified by using 4% PEI ofMW=25,000. The membrane was tested in accordance with the test methoddescribed in Example 1. The results are shown in Table 3.

Example 5

A PAN-GMT-L1 UF support membrane was modified in accordance with theprocedure of Example 1. The procedure was modified by using 4% PEI ofhigh molecular weight (MW=750,000). The membrane was tested inaccordance with the test method described in Example 1. The results areshown in Table 3.

Example 6

A solvent stability test of PAN-GMT-L1 UF support membranes, modified inaccordance with the procedures of Examples 1, 3, 4 and 5 was carried outby placing the membranes in organic solvents for a period of 1 week.After this exposure, the membranes were removed and their performancewas measured using the test method described in Example 1, but using theorganic solvents in which they were immersed instead of ROW.

The results for the membranes' performance are summarized in Table 3,which demonstrates the possibility of using different types of PEI (e.g.of MW=800, 25,000, 750,000) for membrane modification. As observed fromTable 3, solvent resistant UF membranes can be achieved not only withPEI of low molecular weight but also with a higher molecular weight PEI.Using PEI with different molecular weights in the modification processinfluences membrane performance.

TABLE 3 Permeability (L/m2*h*bar) Before PEI modified solvent PAN/UFtreatment Solvent treatment Membrane (ROW) Ethanol Acetone Toluene *Hexane Example1 11 10 15 11 3 16 PEI MW = 800/ 750,000(50:50) Example316 15 45 31 2 101 PEI MW = 800 Example4 13 17 15 4 2 2 PEI MW = 25,000Example5 4 3 7 2 1 10 PEI MW = 750,000 *N-methylpyrrolidone

Example 7

A PAN-GMT-L1/UF support membrane was modified by immersion in a 4%polyethylenimine (PEI) solution (2% PEI, MW=750,000; 2% PEI, MW=800)followed by a heat-treatment in a reactor at 90° C. for 17 hrs. Then themembrane was washed with ROW at room temperature for 1 hr and themembrane was dried by air flow at 90° C. for 1 hr, and then finallywashed.

Example 8 Step 1

PAN-GMT-L1 UF membranes, modified according to the procedure of Examples1 and 7, were placed in a 20% sulfuric acid solution at 90° C. for aperiod of 24 hours. After this exposure, the membranes were removed andtheir performance was measured using the test method of example 1.

Step 2

Thereafter the membranes of step 1 above, as well as PAN-GMT-L1 UFmembranes modified according to the procedure of Examples 1 and 7 thatdid not undergo acid exposure, were placed in organic solvents for aperiod of 1 week. After this exposure, the membranes were removed andtheir performance was measured using test method of example 1 but usingthe above organic solvents.

The results for the membrane performance are summarized in Table 4,which demonstrates the results of differences in the drying process ofthe membrane preparation. As observed from Table 4, the membranes madeaccording to Examples 1 and 7 in different solvents and afteracid-treatment, are UF membranes which are solvent and acid stable. Itcan be concluded that the membrane that was dried immediately afterimmersion in PEI solution (Example 1) is denser then the second membrane(Example 7) and has a lower permeability.

TABLE 4 Permeability (L/m2*h*bar) Before solvent PAN/UF treatmentSolvent treatment Membrane (ROW) Ethanol Acetone Toluene * Hexane PEIWithout 11 10 15 11 3 16 modified acid PAN/UF treatment membrane Withacid 8 11 14 NT 3 20 (Example1) treatment PEI Without 21 23 88 64 2 110modified acid PAN/UF treatment membrane With acid 12 24 75 NT 2 116(Example 7) treatment *N-methylpyrrolidone

Example 9

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1, but was exposed to room temperature for 17 hrs instead ofheat treatment in a reactor at 90° C. The results for the membrane'sperformance, measured in accordance with the procedure described inExample 6, as well as the results for the unmodified commercial membraneand the modified PAN-GMT-L1 membrane as produced in Example 1, aresummarized in Table 5, which demonstrates the importance of theheat-treatment in a reactor at 90° C. for 17 hrs in the process of themembrane preparation. Table 5 shows that the membrane prepared accordingto Example 9 has a lower solvent stability as compared to the membraneprepared in Example 1 and dissolves after exposure toN-methylpyrrolidone, similar to the unmodified commercial PAN/UF supportmembrane.

TABLE 5 Permeability (L/m2*h*bar) Before solvent PAN/UF treatmentSolvent treatment Membrane (ROW) Ethanol Acetone Toluene * HexanePAN-GMT- 109 98 236 50 Dis- 91 L1 solved PEI modified 50 43 125 24 Dis-88 PAN/UF solved membrane (Example9) PEI modified 11 10 15 11 3 16PAN/UF membrane (Example1) *N-methylpyrrolidone

Example 10

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1, except that the heat-treatment in the reactor was carried outfor 5 hours instead of 17 hours. This membrane was tested by the testmethod described in Example 1 and was found to have a permeability inROW of 26 L/m2*h*bar, which indicates less cross-linking of the PAN UFmembrane by PEI.

This membrane was then tested by the method described in Step 1 ofExample 8 and found to have a permeability in ROW of 30 L/m2*h*bar.Finally, the membrane was tested by the method described in Example 2and found to have a permeability in ROW of 31 L/m2*h*bar. These resultsdemonstrate the stability of a membrane performance by showing thesimilar permeability in ROW after exposure to acid and solventtreatment. These results also demonstrate that the procedure describedin this Example gives a solvent and acid stable UF membrane.

Example 11

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1, except that the heat-treatment in the reactor was carried outfor 32 hours instead of 17 hours. The resulting membrane performedsimilarly to the membrane in Example 1. These results demonstrate thatthe procedure described in this example provides a solvent and acidstable UF membrane

Example 12

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1, except that the heat-treatment in the reactor was carried outfor 72 hours instead of 17 hours. This membrane was tested by the testmethod described in Example 1 and found to have a permeability in ROW of120 L/m2*h*bar. The membrane collapsed after being tested by the methoddescribed in Step 1 of Example 8. These results indicate that excessiveheat-treatment time leads to a non-viable membrane.

Example 13

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1. The procedure was modified by using 2% polyethylenimine (PEI)(1% PEI, MW=750,000; 1% PEI, MW=800) instead of 4% polyethylenimine(PEI) (2% PEI, MW=750,000; 2% PEI, MW=800). This membrane was tested bythe test method described in Example 1 and found to have a permeabilityin ROW of 26 L/m2*h*bar, which indicates less cross-linking of the PANUF membrane by PEI than the membrane of Example 1.

This membrane was tested by the method described in Step 1 of Example 8and found to have a permeability in ROW of 54 L/m2*h*bar, and thentested by the method described in Example 2 and found to have apermeability in ROW of 37 L/m2*h*bar. These results demonstrate thestability of the modified membranes after treatment with solvents andacid.

Example 14

A PAN-GMT-L1 UF membrane was modified according to the procedure ofExample 1, but modified by using 10% polyethylenimine (PEI) (5% PEI,MW=750,000; 5% PEI, MW=800) instead of 4% polyethylenimine (PEI) (2%PEI, MW=750,000; 2% PEI, MW=800). This membrane was tested by the methoddescribed above and found to have a permeability in ROW 150 L/m2*h*bar.This membrane collapsed after being testing by the method described inStep 1 of Example 8. The high permeability value and instability in acidindicate the non-viability for present purposes of the membrane by theprocess of this Example, due to excessive concentration of PEI.

Example 15

A PVDF-GMT-L9 UF support membrane purchased from GMT MembrantechnikGmbH, Rheinfelden, Germany was modified according to the procedure ofExample 1. The membrane was tested in accordance with the test methoddescribed in Example 1. The results are shown in Table 6.

Example 16

A PVDF-GMT-L9 UF support membrane was modified according to theprocedure of Example 7. The membrane was tested in accordance with thetest method described in Example 1. The results are shown in Table 6.

Example 17

Membranes were prepared according to the procedure of Examples 15 and16. These membranes were then tested by the method described in Example6. The results for the membrane performance are summarized in Table 6,which demonstrates solvent stability of the new PEI modified UFmembranes and also the effect of differences in the drying process inthe membrane preparation.

Table 6 shows the performance of the membrane as made according toexamples 15 and 16 in different solvents compared to commercial PVDF/UFsupport membrane. A commercial PVDF/UF support membrane shows a veryhigh permeability in organic solvents that indicate their instability inthe tested solvents. On the other hand, the new PEI modified UFmembranes have a good stability in different organic solvents. Inaddition, a membrane dried immediately after immersion in PEI solution(Example 15) is denser then the second membrane (Example 16) and haslower permeability.

TABLE 6 Permeability (L/m2*h*bar) Before solvent PVDF/UF treatmentSolvent treatment Membrane (ROW) Ethanol Acetone Toluene Hexane PVDF-GMT2 818 543 3182 3864 PEI modified 6 9 9 8 33 PVDF-GMT membrane (Example15) PEI modified 16 21 45 23 36 PVDF-GMT membrane (Example 16)

Example 18

PES/UF support membranes (Nadir UP020 purchased from Microdyn-NadirGmbH, Weisbaden, Germany, and Sepro PES-20 purchased from SeproMembranes, Inc., Oceanside, Calif., USA) were functionalized byimmersion in a solution of 5% (v/v) chlorosulfonic acid in glacialacetic acid at a room temperature for 1 hour. Then the membranes werewashed by cool (0-5° C.) RO water for 30 min.

Example 19

PES/UF support membranes prepared according to Example 18 were modifiedand tested according to the procedures of Example 1. The result ofmodification of different commercial PES/UF support membranes issummarized in Table 7, which demonstrates that the modification by PEIgives a new UF membrane with a different membrane performance.

TABLE 7 Type of commercial Before modification After modification PES/UFsupport Permeability Permeability membrane (L/m2*h*bar)/ROW(L/m2*h*bar)/ROW Nadir UP020 77 6 Sepro PES-20 118 8

Example 20

Membranes prepared according to the procedure of Example 19 were placedin acetone for a period of 1 week. After this exposure, solvent teststability for the PES membrane was carried out using the test method ofExample 1 and permeabilities in ROW of 7 L/m2*h*bar and 8 L/m2*h*bar fora modified membrane formed using a Nadir UP020 support membrane and fora modified membrane formed using a Sepro support membrane, respectively,were found. A commercial unmodified PES/UF support membrane dissolvedimmediately after immersion in acetone. These results demonstrate thestability of the modified membranes in a solvent.

Example 21

Membranes prepared according to the procedure of Example 19 were placedin a 20% aqueous sulfuric acid solution at 90° C. for a period of 24hours. After this exposure, the membranes were removed and theirperformance was measured using the test method described in Example 1.Permeabilities in ROW of 8 L/m2*h*bar and 10 L/m2*h*bar for a modifiedmembrane formed using a Nadir UP020 support membrane and for a modifiedmembrane formed using a Sepro support membrane, respectively, werefound. These results demonstrate the stability of the modified membranesin the presence of acid.

Example 22

A Sepro PES-20/UF support membrane was functionalized by immersion inaqueous solution of 3% (w/v) ammonium persulfate and heated to 90° C.for 10 minutes. Then the membrane was washed by RO water for 30 min andimmersed in a cooled (5-7° C.) aqueous solution of 0.1% (w/v) cyanuricchloride for 1 hour. The resulting membrane was washed in cooled ROwater.

Example 23

A PES/UF support membrane prepared according to Example 22 was modifiedaccording to the procedure of Example 1. The finished membranemaintained its performance after immersion in acetone for 24 hours, asopposed to the commercial unmodified support membrane that dissolvedwithin minutes after being immersed in acetone.

Example 24

A Sepro PES-20/UF membrane was functionalized by ozone oxidation for 5min. Then the membrane was washed with RO water for 30 min and immersedin cooled aqueous solution of 0.1% (w/v) cyanuric chloride at 5-7° C.for 1 hour. The resulting membrane was rinsed in cooled RO water.

Example 25

A PES/UF support membrane prepared according to Example 24 was modifiedaccording to the procedure of Example 1. The finished membranemaintained its structural integrity after immersion in NMP for 4 hours,as opposed to a commercial unmodified support membrane that dissolvedwithin minutes after immersion in NMP.

It will be appreciated that the PES membranes can be functionalized byother methods, such as those described in the following theoreticalexamples 26 and 27. The membranes thus formed are expected to have thesame properties as the membranes formed in Examples 18-25.

Example 26

A PES/UF support membrane is treated in air by corona dischargeequipment. Then the membrane was washed with RO water for 30 min,immersed in cooled aqueous solution of 0.1% (w/v) cyanuric chloride at5-7° C. for 1 hour, and rinsed again in cooled RO water. The membranethus prepared is modified according to the method described in Example1.

Example 27

A PES/UF support membrane is placed vertically in the vacuum chamber ofplasma equipment fitted with parallel electrode plates and evacuated toa base pressure lower than 2*10⁻⁵ mbar. Then ammonia gas is introducedat 15 cm³/min into the chamber, and plasma treatment is performed for 20min as described in Applied Surface Science, 253, Issue 14, 2007, P.6052-6059, You-Yi Xu et al.

The resulting modified membrane, now having amine groups on the surfacethereof is immersed in a cooled 5-7° C. aqueous solution of 0.1% (w/v)cyanuric chloride for 1 hour. The resulting membrane is washed in cooledRO water. The membrane thus prepared is modified according to the methoddescribed in Example 1.

Example 28

A monolithic solvent and acid resistant PVDF/UF membrane was preparedaccording to the following procedure. A non-woven polypropylenesubstrate (PP) was immersed in 934-0-1 Kunststoff-Haftprimer (primer forPP to make it reactive; Glasurit, Munster, Germany), for 1 min at roomtemperature, and then dried for 10 min at room temperature and foranother 10 min at 70° C. After that, the PP was modified by immersion ina 2% polyethylenimine MW=800, followed by heat-treatment at 90° C. for 5hrs. The PP was washed with ROW at room temperature for 1 hr and finallydried. Casting of a PVDF/UF membrane was carried out according to theprocedure that was described in EP 0574957, followed by heat-treatmentat 90° C. for 5 hrs. Preparation of the monolithic solvent and acidresistant PVDF/UF membrane on the integral PP substrate was completedaccording to the procedure of Example 1.

Examples 29-31 illustrate syntheses of compounds derived fromhalodiazines and halotriazines that may be used as halogenated di- ortriazines in the preparation of membranes for use in accordance withembodiments of the invention.

Example 29 Preparation of Condensate of p-Anilinesulfonate andDichlorotriazine

6 g of NaOH were dissolved in 150 ml of water that had been filteredthrough a reverse osmosis unit (“RO water”) followed by addition of 0.15mol of sulfanilic acid and adjusting the pH to above 12 by addition ofNaOH as necessary. 50 ml of 3M NaOH were added to this solution ofsulfanilic acid and the resulting solution was added to an aqueoussuspension of 0.15 mol of cyanuric chloride and left in a magneticallystirred vessel for 4 h at a temperature of 4-7° C. at pH˜10. Theproduct, which precipitated from the reaction mixture, was washed withacetone and RO water prior to use.

Example 30 Preparation of Condensate of p-Anilinesulfonate andDibromotriazine

6 g of NaOH are dissolved in 150 ml of RO water followed by addition of0.15 mol of sulfanilic acid and adjusting the pH to above 12 by additionof NaOH as necessary. 50 ml of 3M NaOH were added to this solution ofsulfanilic acid and the resulting solution was added to an aqueoussuspension of 0.15 mol of cyanuric bromide and left in a magneticallystirred vessel for 4 h at a temperature of 4-7° C. at pH˜10. Theproduct, which precipitates from the reaction mixture, is washed withacetone and RO water prior to use.

Example 31 Preparation of Condensate of Two Substituted Triazole Groupswith Amine Bridge

Step 1: 6 g of NaOH are dissolved in 150 ml RO water followed byaddition of 0.15 mol of 1,3-diaminopropane and adjusting the pH to above12. 50 ml of 3M NaOH were added to this solution of sulfanilic acid, andthe resulting solution was then added to an aqueous suspension of 0.15mol cyanuric chloride and reacted for 4 hours at a temperature of 4-7°C. at pH˜10. The product, which precipitates from the reaction mixture,is washed with acetone and RO water.

Step 2: 6 g of NaOH are dissolved in 150 ml RO water followed byaddition of 0.15 mol of the product from step 1 and adjusting the pH toabove 12. Subsequently, an additional 50 ml of 3M NaOH and an aqueoussuspension of 0.15 mol cyanuric chloride are added and reacted for aperiod of 4 h at temperature of 4-7° C. at pH˜10. The product, whichprecipitates from the reaction mixture, is washed with acetone and ROwater prior to use.

Example 32 Preparation of Non-Monolithic Membrane on a PS UF SupportMembrane

A membrane suitable for use in accordance with embodiments of theinvention was prepared in the following manner. A polysulfoneultrafiltration support membrane formed on a polypropylene nonwovensubstrate supplied by FuMA Tech, termed “PES 006 cutoff” having amolecular weight cut-off (measured by the ASTM method at 90% dextranrejection) of 6000 Daltons was subjected to a cleaning step with ROwater for 1 hour, then was rinsed with 0.3% solution of sodium dodecylsulfate (SDS) and subsequently rinsed with RO water until no traces ofSDS remained. The rinsed membrane was inserted into a pressure cell andcontacted for 30 minutes at 10 bars with an aqueous reaction solutionconsisting of (a) a 0.125% aqueous solution of branched polyethyleneimine (PEI) (Aldrich, M_(w)=750,000 as determined by gel permeationchromatography), and (b) a 0.075% aqueous solution of a condensateprepared from cyanuric chloride and sulfanilic acid as per Example 29.The excess modification solution was then drained, and the resultantmembrane was removed from the pressure cell and heated at 90° C. for 30min in a convection oven. After curing, the membrane was placed in a 20%aqueous ethanol solution containing 0.1% w/w of the condensate ofcyanuric chloride and sulfanilic acid formed in Example 29. The solutionwas heated to 60° C. and the membrane was treated in this solution for aperiod of 1 hour in order to complete the cross-linking reaction step.After this reaction step the membrane was removed form the reactionvessel and rinsed in RO water for a period of 1 hour. After rinsing themembrane with RO water the membrane was placed in 20% solution ofsulfuric acid in water at 90° C. for a period of 5 hours in order tohydrolyze all reactive chloro groups of the cyanuric chloridecondensate. The membrane was removed from the acid, rinsed with RO waterovernight, removed and subjected to a subsequent testing session.

Analogous membranes may be prepared, for example, by substitutingcyanuric fluoride or cyanuric bromide for cyanuric chloride in thecondensate with sulfanilic acid (e.g. by using the condensate product ofExample 30 instead of the product of Example 29) or, for example, byusing a condensate of two substituted triazole groups with an aminebridge (e.g. by using the condensate product of Example 31 instead ofthe product of Example 29).

Test Method 2:

Membrane performance (permeability and solute rejection) was measuredusing a magnetically stirred test cell at a pressure of 40 bar suppliedfrom a compressed nitrogen gas cylinder. The cell was a stainless steelcylinder having at its bottom a sintered stainless metal platesupporting the membrane. For the permeability measurement, reverseosmosis water (ROW) was introduced to the test cell and permeate wasallowed to accumulate and measured versus time. For the solute (glucose)rejection measurements, the test cell was filled with a 5% solution ofglucose in water. The permeate was allowed to accumulate and its glucoseconcentration was measured by means of refractometry.

Afterwards the membrane was placed in a 20% sulfuric acid solution at90° C. for a period of 180 hours. After this exposure, the membraneperformance was tested again. The rejection (calculated according toaccepted procedures known to those skilled in the membrane field) ofglucose before sulfuric acid immersion was 97.5% and after immersion was98%. Water flux before sulfuric acid immersion was 800 liters/m²*day,and after the prolonged immersion in hot acid it was 950 liters/m²*day.These results demonstrate superior stability of the NF membrane in acidconditions.

Example 33

The membrane and test procedure were repeated as in Example 32, thistime increasing the immersion time of the membrane in 20% sulfuric acidat 90° C. from 180 hours to 360 hours. The measured rejection after 360hours was 40% and the flux was 1700 liters/m²*day. This result indicatesthat while membranes prepare per Example 29 exhibit significantstability in acid, this stability is limited in time.

Example 34

A monolithic NF membrane (i.e. in which the NF matrix is covalentlybound to the UF support membrane, and the UF layer is covalently boundto its substrate) having dimensions of 30 cm by 25 cm was prepared froma UF support membrane having cross-linked polyacrylonitrile. PAN UFmembranes were prepared according to the procedure described in Example1.

To prepare an NF membrane for use in accordance with embodiments of thepresent invention, these modified UF membranes containing active aminogroups were then coated by doctor knife with predetermined slitthickness of 50 microns, using a reactive coating solution containing0.1% of PEI (Example 32 above) and containing a similar concentration ofa condensate of cyanuric chloride with sulfanilic acid as described inExample 29 above. After coating, the membrane was completely dried inair and immersed for a curing step in an oven at 90° C. for 1 hour.After this step the membrane was immersed in a 20% aqueous ethanolsolution containing 0.02% w/w of the condensate of cyanuric chloride anda sulfanilic acid of Example 29. The solution was heated to 60° C. andthe membrane was treated in this solution for a period of 1 hour inorder to complete the cross-linking reaction step.

The membrane was then immersed in 20% sulfuric acid at 90° C. for aperiod of 340 hours and its performance was tested periodically duringthis period. As shown in FIG. 8A, the rejection to glucose remained inthe range of 95-99%, and the fluxes increased during this period from˜1000 liters/m²*day to ˜2000 liters/m²*day, without any adverse affecton the rejection.

Example 35

A monolithic NF membrane was prepared as described in example 34 above,but utilizing as UF support membrane a cross-linkedpolyvinylidenefluoride (PVDF) membrane prepared in accordance withExample 15. The NF membrane was then immersed in a 75% concentratedsulfuric acid at 60° C. for a period exceeding 1100 hours. In addition,a commercially available polysulfonamide acid-stable NF membrane (KHmembrane purchased from Osmonics, Inc., Minnetonka, Minn., USA) wasimmersed in the same solution and tested periodically. The results areshown in FIG. 8B. The KH membrane had an initial rejection of glucose of98%, but after about 200 hours the rejection declined to ˜80% and afteran additional 200 hours the rejection dropped to 70%, showing itsinstability in such conditions. In contrast, the monolithic NF membranemaintained high rejection throughout the entire testing period, withfluxes stabilizing around 1500 liters/m²*day.

Example 36 Separation of Metal Ions from Acidic Feed Stream

A membrane prepared according to example 35 was rolled into a spiralwound element 2.5 inches in diameter and 14 inches in length and thenassembled into a pressure vessel. The pressure vessel was installed in atest system equipped with a feed vessel of 20 liters, a pump providing acirculation flow rate of up to 20 liters/minute and a pressure of up to40 bars. The feed tank was filled with copper-containing acid leachateprovided by a copper mine in Chile. The concentrations of the main metalions (copper, aluminum and iron) were measured and are reported in Table8. The pH of the stream was ˜1. The stream was circulated under pressureallowing permeate to pass across the membrane. The volume of the feedstream was maintained at 20 liters using fresh feed. A total of 80liters of feed water were processed, so that this volume wasconcentrated 4-fold to a volume of final concentrate of 20 liters. Thusthe volumetric concentration factor (VCF) was 4. The copperconcentration in the concentrate and in the permeate was measured by ICPspectrometry by an external laboratory. The results are shown in Table8.

TABLE 8 Copper Flux Composition Concentration in ppm rejec- Liters/ offeedwater Feed concentrate Permeate tion % m²*day Cu 450 1840 1.6 99.9%480 Al 30 0.04 Fe 2 0

As observed, very high copper retention was demonstrated in these tests.The experiment continued by circulating the concentrate in a closed loopfor a period of 4 weeks in order to observe any change in performance.The results after 4 weeks of operation remained practically unchanged.

Example 37 Preparation of High Flux NF Membranes Using Reactive Dyes

A monolithic High Flux NF membrane sample having dimensions of 30 cm by25 cm was prepared starting from a cross-linked polyacrylonitrile (PAN)UF support membrane, the preparation of the PAN UF support membrane isdescribed in Example 1 above. To prepare the NF membrane, the UFmembrane, which contained active amino groups, was immersed in anaqueous solution of 1% dye of Formula I shown below and 10% sodiumchloride for 15 min and then in 5% solution of Na₂CO₃ for 20 minutes.This resulted in a modified UF membrane that served as a support for thesubsequent NF layer. The NF layer was formed by coating the modified UFmembrane, using a doctor knife having a slit thickness of 50 microns,with a reactive aqueous polymer solution containing 0.1% PEI and anequal concentration of a condensate of cyanuric chloride with sulfanilicacid, prepared as described in Example 29 above. The coated membrane wasdried in air and then cured for 1 hour in an oven at 90° C. After thisstep the membrane was immersed in a 20% aqueous ethanol solutioncontaining 0.02% w/w of the condensate of cyanuric chloride and asulfanilic acid and heated for 1 hour at 60° C. The membrane sampleswere tested by Test Method 2. The water flux was 1800 liters/m²*day andglucose rejection was 98%.

Example 38 Solvent Stability of NF Membranes Made Using Reactive Dyes

A membrane prepared according to the procedure of Example 37 was testedin a 5% aqueous glucose solution and immersed in N-methylpyrrolidone fora period of 8 days. After this exposure, the membrane was removed,washed in RO water for 24 hours and tested as described in Test Method2. The glucose rejection before the immersion in organic solvent was98.6% and remained high after immersion at a level of 98%. Water fluxbefore organic immersion was 1800 liters/m²*day (LMD), and after theimmersion in organic solvent it was 1400 liters/m²*day.

Example 39 Solvent Stability of Monolithic PAN Membrane

Several membrane samples that were prepared according to the procedureof Example 34 were tested in a 5% aqueous glucose solution. Afterwardthe membranes were immersed for different time periods in severalorganic solvents, such as N-methylpyrrolidone (NMP), dimethylformamide(DMF) and acetone. After the exposure, the membrane was removed, washedin RO water for 24 hours and tested as described in Test Method 2. Theresults of the membrane performances are summarized in Table 9. Theresults demonstrate high stability in presence of organic solvents.

TABLE 9 INITIAL PERFORMANCE SOLVENT TREATMENT Water Glucose Water flux5% Solvent Temp, Exposure flux Glucose (LMD) Rejection type ° C. Time,day (LMD) Rejection 1505 98.3 NMP RT 13 1200 98.4% NMP RT 304 1450 98.2%DMF RT 300 1420 98.1% Acetone RT 300 1470 99.0%

Example 40 Alkaline Stability of Monolithic PAN Membrane

Several membrane samples that were prepared according to the procedureof Example 34 were tested in a 5% aqueous glucose solution. Afterwardthe membranes were immersed for different time periods in 10% and 20%NaOH solutions respectively. The membranes were tested according to theTest method. The results of the membrane performances after exposure aresummarized in Table 10 (performance before exposure was similar to thatshown in Table 9).

TABLE 10 NAOH TREATMENT, RT Exposure Time, Water flux Glucose conc.NaOH, % hours (LMD) Rejection 10 18 1300 99.0% 10 42 1520 98.5% 20 481300 99.0%

Example 41 Preparation of NF Membranes on Polyethersulfone (PES)(Monolithic and Non-Monolithic)

A. An NF membrane was prepared according to the procedure of Example 32,but a polyethersulfone (PES) UF support membrane (Microdyn Nadir UP020)was used instead of a polysulfone (PS) support membrane.

B. A monolithic NF membrane (30 cm by 25 cm) in which the NF top layeris covalently bound to the underlying PES UF support membrane,containing covalently bound amino groups, was prepared from anunderlying PES support membrane that itself was prepared as described inExample 19. Specifically the PES UF membrane was prepared by modifying acommercially available PES UF membrane by first functionalizing it byimmersion in a 5% (v/v) solution of chlorosulfonic acid in CHCl₃/CCl₄(1:1) at room temperature for 1 hour. The membrane was then washed withcool (0-5° C.) RO water for 30 min. The resulting UF membrane wasfurther modified as described in Example 1, viz. by immersion in a 4%aqueous PEI solution (2% PEI, MW=750,000, 2% PEI MW=800) followed byheat-treatment in a reactor at 90° C. for 17 h, followed by drying underair flow at 90° C. for 1 h and washing with RO water.

This UF support membrane was then coated by a doctor knife with a 50micron thick layer of a reactive polymer solution containing 0.1% of PEIand an equal concentration of a condensate of cyanuric chloride withsulfanilic acid prepared as described in Example 29 above. Aftercoating, the membrane was dried in air and subsequently cured for 1 hourin an oven at 90° C. After this step the membrane was immersed in a 20%aqueous ethanol solution containing 0.02% w/w of the condensate ofcyanuric chloride and a sulfanilic acid. The solution was heated to 60°C. and the membrane was treated in this solution for a period of 1 hour.

Example 42 Acid Stability of PES Membranes (Monolithic andNon-Monolithic)

NF membranes prepared as described in Example 41 were immersed in a 20%sulfuric acid at 90° C. for a period of 1-20 hours. These membranes weretested as described in Test Method 2. The results of the membraneperformances are summarized in Table 11, demonstrating superior acidstability of the monolithic NF membrane compared to that of the NFmembrane in which the top layer is not covalently bound to theunderlying UF support membrane.

TABLE 11 Performance after 20% H₂SO₄ treatment, 90° C. Membrane Acidexposure Water flux Glucose 5% preparation time, hours (LMD) RejectionExample 41A 1 450 95% 18 2650 75% Example 41B 1 950 94% 20 1710 94%

Example 43 Alkaline Stability of Monolithic PES Membranes

Several membranes prepared in accordance with the procedures of Examples41A and 41B were immersed for different durations in a 4% NaOH solution.These membranes were tested as described in Test Method 2. While themonolithic membrane (41B) maintained initial performance after alkalineimmersion for a period of 7 days, the standard non-monolithic membrane(41A) showed a decline in glucose rejection values from an initial valueof 95% to 75% after 7 days.

Example 44 Preparation of Non-Monolithic NF Membrane on a PAN UF SupportMembrane

A PAN-GMT-L1 UF support membrane was treated with a 10% aqueous solutionof sodium hydroxide at 50° C. for 15 minutes, washed well with water andheated for 15 minutes at 110° C. in a high boiling solvent such asglycerol. Afterward, the membrane was washed with RO water. It wascoated, using a doctor knife having a slit thickness of 50 microns, witha reactive polymer solution containing 0.1% of PEI and an equalconcentration of a condensate of cyanuric chloride with sulfanilic acid,prepared as described in Example 29 above. The coated membrane was driedin air and subsequently cured for 1 hour in an oven at 90° C. After thisstep the membrane was immersed in a 20% aqueous ethanol solutioncontaining 0.02% w/w of the condensate of cyanuric chloride and asulfanilic acid. The solution is heated to 60° C. and the membrane wastreated in this solution for a period of 1 hour.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of various featuresdescribed hereinabove as well as modifications thereof which would occurto a person of skill in the art upon reading the foregoing descriptionand which are not in the prior art.

The invention claimed is:
 1. A polymeric semipermeable membranecomprising a non-cross-linked base polymer having reactive pendantmoieties, said base polymer being modified by forming a cross-linkedskin onto a surface thereof, said skin being formed by a cross-linkingreaction of reactive pendant moieties on said surface with across-linking oligomer or another polymer thereby, said base polymer iscovalently bonded to said oligomer or another polymer; wherein said basepolymer is polyacrylonitrile (PAN) such that at least one portion ofsaid cross-linked skin of said base polymer is covalently bonded to ananofiltration layer by immersion of said cross-linked skin of said basepolymer in polyethylenimine (PEI) and condensate solution comprisingcyanuric chloride and sulfanilic acid thereby, said polymericsemipermeable membrane having acid and organic solvent stability; saidnanofiltration layer comprises (i) at least one di-, tri- or tetra-halosubstituted diazine or triazine-containing monomer, oligomer or polymer,and (ii) at least one multifunctional amine having a molecular weight inthe range of 400 to 750,000.
 2. The polymeric semipermeable membraneaccording to claim 1, wherein additionally comprising a woven or nonwoven substrate underlying said base polymer.
 3. The polymericsemipermeable membrane according to claim 1, wherein said base polymeris selected from polyacrylonitrile and copolymers thereof.
 4. Thepolymeric semipermeable membrane according to claim 1, wherein saidanother polymer is selected from polyethylenimine and polyvinyl alcohol.5. The polymeric semipermeable membrane according to claim 1, whereinsaid polymeric semipermeable membrane is an ultrafiltration membrane ora microfiltration membrane.
 6. A nanofiltration (NF) membrane havingstability in acid and organic solvents, said NF containing a matrix thathas been formed from a solution comprising PEI and a condensatecomprising cyanuric chloride and sulfanilic acid; said matrix was driedat elevated temperature thereby, forming a matrix comprising (i) atleast one di-, tri- or tetra-halo substituted diazine ortriazine-containing monomer, oligomer or polymer, and (ii) at least onemultifunctional amine having a molecular weight in the range of 400 to750,000.
 7. The NF membrane of claim 6, wherein said matrix has beenformed on an underlying ultrafiltration or microfiltration membrane. 8.The NF membrane of claim 7, wherein the underlying membrane is amodified ultrafiltration membrane by forming a cross-linked skin onto asurface thereof; said modified ultrafiltration is covalently attached toa support material.
 9. The NF membrane of claim 8, wherein the supportmaterial is a non-woven support material.
 10. The NF membrane of claim6, wherein said diazine or triazine-containing monomer or oligomer isselected from the group consisting of:

wherein: R¹ is independently selected at each occurrence from bromo,chloro, iodo, fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵ is independentlyselected at each occurrence from H, optionally substituted alkyl andoptionally substituted aryl; R² is independently selected at eachoccurrence from bromo, chloro and fluoro; R³ is independently selectedat each occurrence from bromo, chloro, fluoro, —NHR⁵, —OR⁵ and SR⁵,wherein R⁵ is independently selected at each occurrence from H,optionally substituted alkyl and optionally substituted aryl; R⁴ isselected from H, bromo, chloro, fluoro, —NHR⁵, —OR⁵ and SR⁵, wherein R⁵is independently selected at each occurrence from H, optionallysubstituted alkyl and optionally substituted aryl; and R⁸ isindependently at each occurrence —NH-A-NH—, wherein A is selected fromC₁₋₂₀ aliphatic moieties, C₆₋₁₀ aromatic moieties, and combinationsthereof; provided that at at least two occurrences, R¹, R², R³ and R⁴,taken together, are selected from bromo, chloro and fluoro, and furtherprovided that when both R¹ and R² on a single ring are Cl, at least oneof R³ and R⁴ is not Cl.
 11. The NF membrane of claim 6, wherein saidmultifunctional amine has a molecular weight of in the range of 400 to250,000.
 12. The NF membrane of claim 6, wherein said matrix is formedby a process which comprises providing an asymmetric baseultrafiltration membrane which at one face thereof has pores of smallerdiameter than at the opposite face; providing a solution containing atleast one di-, tri- or tetra-halo substituted diazine ortriazine-containing monomer, oligomer or polymer, at least onemultifunctional amine having a molecular weight in the range of 400 to750,000; and bringing the solution into contact with the face of theultrafiltration membrane having smaller pores under superatmosphericpressure for a time sufficient to effect covalent bonding of the atleast one di- or tri-halo substituted diazine or triazine-containingmonomer, oligomer or polymer and the at least one multi-functionalamine.
 13. The NF membrane of claim 12, wherein said solution furthercomprises at least one supplemental cross-linker.
 14. The NF membrane ofclaim 12, wherein prior to said contacting, said ultrafiltrationmembrane has been modified to facilitate covalent bonding to the surfacethereof.
 15. The NF membrane of claim 12, wherein, prior to saidcontacting, the ultrafiltration membrane was modified by forming across-linked ultrafiltration skin on the surface thereof, on which thematrix is then formed.
 16. The NF membrane of claim 12, wherein theformation of the matrix further comprises, after said contacting,heating said ultrafiltration membrane.
 17. The NF membrane of claim 12,wherein said multifunctional amine is selected from the group consistingof polyethylenemine, polyvinylamine, polyvinylanilines,polybenzylamines, polyvinylimidazolines, and amine-modifiedpolyepihalohydrins.
 18. The NF membrane of claim 13, wherein saidsupplemental cross-linker is selected from the group consisting of2,4,6-trichloro-s-triazine, 4,6-dichloro-2-sodiump-sulfoanile-s-triazine (4,6-dichloro-2-p-anilinesulfonic acid sodiumsalt-s-triazine), 4,6-dichloro-2-diethanolamine-s-triazine and4,6-dichloro-2-amino-s-triazine.
 19. The NF membrane of claim 6, whereinsaid matrix has a density of from about 0.5 g per cm³ to about 2.0 g percm³.
 20. The NF membrane of claim 6, wherein the mass to area ratio ofsaid matrix is from about 20 to about 200 mg/m².
 21. The polymericsemipermeable membrane according to claim 1, wherein said base polymeris preferably polyacrylonitrile.
 22. The polymeric semipermeablemembrane according to claim 1, characterized by having improvedstability in an aggressive environment comprising at least one organicsolvent.
 23. The nanofiltration membrane according to claim 6, whereinafter further exposure of said NF membrane to 75% sulfuric acid at 60°C. for 1000 hours, said NF membrane exhibits a glucose rejection of atleast 95% at a flux of at least 10 gfd.
 24. The nanofiltration membraneaccording to claim 6, wherein after further exposure of said NF membraneto 20% sulfuric acid solution at 90° C. for 180 hours, said membraneexhibits a glucose rejection of 98% at a flux of 950 liters/m*day.
 25. Apolymeric semipermeable membrane having solvents and acids stability,prepared by steps of: a. providing a UF base polymer comprising a crosslinked polyacrylonitrile (PAN) containing active amino groups; b.providing a solution comprising polyethylenimine (PEI) and condensate;said condensate comprising cyanuric chloride and sulfanilic acid; c.immersing said PAN in said solution comprising PEI and condensate,thereby, covalently bonding a Nanofiltration (NF) layer with said UFbase polymer; said NF comprising (i) at least one di-, tri- ortetra-halo substituted diazine or triazine-containing monomer, oligomeror polymer, and (ii) at least one multifunctional amine having amolecular weight in the range of 400 to 750,000; d. curing said membraneby drying at elevated temperature.
 26. The polymeric semipermeablemembrane claim 25, wherein said elevated temperature is in the range of50-100° C.
 27. The polymeric semipermeable membrane claim 25, whereinsaid polyethylenimine (PEI) solution has a concentration between 2%-10%.